Sealing lower trim, water in rocker panels


Well-known member
After 2 months with virtually no rain in Seattle, we finally had some rain in the past couple weeks, some of it pretty heavy. Since my interior lower panels were removed for my work, I noticed some pretty significant water pooling in the bottom of the rocker panels. The water is obviously entering through the plastic trim connectors which hold the black trim that is all around the lower van body.

The 1/8" deep puddles in some spots of my rocker panels occurred without even driving. Just parked on level ground during a solid rain.

I did some searches but couldn't find any threads on this specific topic. Has anyone tried to reduce/eliminate this ingress? If so, how? Sealing the holes/connectors from the inside? Removing trim and doing something on the exterior?

The rocker panels have some pretty thick yellow overcoating and drain holes, so to some extent they are capable of handling water. But if I extrapolate to 10 years of repeated water ingress, I worry that it will lead to corrosion and/or fungus. Already there black tracks where the water trickles in, though its hard to tell if that is fungus or residue/sediment from trim material.



Van Guru
The black stuff is likely just dirt/dust collected behind the trim and then washed inside with the water. We used 3M window weld slathered over each clip where it comes inside. It took a couple applications to get some of them to stop dripping. Spraying undercoat or bed-liner over them doesn't seem to do the trick completely.


Well-known member
We used 3M window weld slathered over each clip where it comes inside.
Applied from the inside, just trying to cover the entire clip and hole?

Was there a rationale for using 3M window weld as opposed to something like Dicor or similar sealant?


Well-known member
Found another puddle today after some persistent rain. This is with the vehicle parked, not driving. Despite having sealed each trim panel plug from the inside with two applications of sealant over a month ago, water is still getting into at least some of the lower wall areas. In particular, the lower wall about 4 feet rear of the driver seat. There was maybe 1/4 cup of water sitting in a puddle just forward of the C pillar. The lower part of my Thinsulate was soggy from sitting in the puddle.

I've glued in Thinsulate since my original observation of water, so I can't inspect each plug very well, but they were HEAVILY sealed with sealant, so I'm surprised one or more of them could be passing this much water. The interior of the outer lower black trim plastic must be holding a substantial amount of water that is leaching through into the van walls over time??

It just seems odd that a brand new 2014 van would permit that much water ingress "by design."


Tooth Fairy

Away with the fairies.


New member
I recall a post and pics of sealant applied at the top of the trim panel outside. Any thoughts against that?


'14 170 4cyl Crew
One way to do this is to remove the black trim pieces and seal under each clip from the outside of the van.

1. Remove the screws holding the ends of the black trim onto the doors. The screws at the rear of the sliding door will require a "right angle" torx bit holder... access here with the door open is only about 4-5 inches. Front door screws are easily seen and accessed.

2. Then, use some "body trim tools" to pry off the black trim from the clips. The trim pulls out from under the rear wheel-well trim. As I recall, the rear-most clip on the sliding door is different than the others... it requires you to pull the trim forward to remove it after it's been popped off from the others.

3. Remove each clip from the body. I found the best way to do this is to insert the "V" notch of the trim tool all the way under the clip... this compresses the legs of the clip so it then can be pried out of its body hole without damage.

Then, seal the underside of each clip and reinstall... I used Sikaflex under each clip. I also sealed the body plugs that were visible.

It helps to do this on a warm day, so the plastic is as flexible as possible. I was able to do this without breaking any of the clips, and no sign of water invasion showed up afterwards.







Well-known member
One way to do this is to remove the black trim pieces and seal under each clip from the outside of the van.
Hmm. This approach is problematic now, given that I have sizable blobs of sealant on the interior side of the clips, so removing the clips isn't a practical option. I suppose I could use a tool to peel up the edge of the clips (on the exterior) and slide it around the circumference of the clip as I inject sealant underneath.


I sealed mine from the inside before closing up the walls. 4 coats of rubberized spray undercoat..


I remember a post but I can never find them either. Also there are other big holes covered with basically circles of paper which clearly fails. Anyone know the part number. Freightliner said they were 15 bucks a piece and Mercedes dealer can't figure out which one it is and if there are a couple.

I see the bag with the numbers I need, thanks


New member
Since it has been about a year since this thread was active, I am wondering how each of these options turned out? Anybody have any leaks?
We are trying to decide whether to seal from the inside or the more laborious job of removing the trim and sealing from the outside. And if we do go from the outside we are nervous about breaking clips. Kinda looks like its best to buy new ones?
Thanks in advance!


2013 144
I pulled the trim and sealed the fasteners with caulk while they were on the trim, and then put them back. I've recently pressure washed the van a few times, and no water in the spots that I have checked. The only thing I would do differently is to run a bead of caulk along the inside upper edge of the trim - lots of dirt and soapy water gets behind the trim. Sealing the upper edge should help that.

Removing wasn't really laborious - a pair of needle-nose pliers squeezed the tabs on the inside, and they popped right out. There were a few that I couldn't reach and used trim tools from the outside; no breakage.

Sent from my iPad using Tapatalk
This thread is very timely for me as well. I opened up a wall panel to run some additional wiring and found it damp and musty. Additionally, my insulation appears to have been wicking up some of the moisture. Total pain in the ass, but I'm really glad I found it now instead of in a few years when my walls started rusting.

Thanks to those who written about this issue!

We've finally had some significant rain here in Northern California, and The van hasn't been driven much in the last few weeks. I suspected it was the trim panel plugs, but this thread has helped me so much! Turned a mystery leak into a relatively easy fix.

I will post up some pics once I get the leak confirmed and sorted out!

I will likely have to use caulk from the inside to resolve the problem. Not my preferred solution, but my time constraints don't allow me to pull all the trim from the outside. If I had more time, I would do it properly from the outside.

This seems kind of ridiculous for this to be a common problem for a Mercedes.

Thanks everyone!


On A Journey
My Texas Sprinter is not sure what to make of the Pacific NorthWet.

Thanks for bringing this thread to the top, timely as I have been wondering what to do. Thanks to all who have added advice here.
A huge thank you to everyone who contributed to this. Very timely for me since I discovered a nearly 100% failure rate on the upper row of trim panel clips. I had water pooling in every lower wall panel because of Mercedes ridiculous cheap trim panel clips. It's really shameful- especially since a permanent solution to this would probably only cost Mercedes a few dollars.

I suspect that this moisture intrusion into sealed walls contributes heavily to premature rust!

I did a complete blog post with lots of pics. You can check it out here.


Leaking into Sprinter cabin space- a cautionary tale of terrible design

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