Main rear seal leak - worth addressing?

eranrund

Active member
Hello!

My mechanic told me today I have a leak at the rear main seal, and in their opinion it is okay to wait with fixing it.
Fixing it involves taking off the transmission, which isn't cheap (quoted ~$1K - the bay area is expensive...). I'm wondering how to make a decision on this. I will degrease the area so I could monitor the leak, but am wondering what do others think?
I tried searching the forum and it seems like this is a relatively rare problem. Is it possible the leaky seal is a symptom of a different problem?
How likely is it that taking off the transmission and flywheel, and then replacing the seal, would do more harm than good? While the mechanic place is very reputable and I have had good experience with them so far, I am not sure how many sprinters they get to work on and it would suck if I ended up with a bigger problem.

Thanks and have a good long weekend!!
 

Midwestdrifter

Engineer In Residence
Check your crankcase breather. Any other leaks? If your oil consumption is reasonable, you can likely just roll it.
 
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220629

Well-known member
They sound like they're not trying to up sell. I would listen to them.

Assuming you don't have some annual environmental inspection that includes no dripping leaks... There's nothing wrong with watchful waiting. If the amount of visible oil increases go back to your shop.

:2cents: vic
 

eranrund

Active member
Thank you for the replies. Where do I see the crankcase breather? Is that the open-ended hose thats dangling around the transmission area?
My oil consumption has been reasonable, I would monitor it more carefully going forward.
 

Midwestdrifter

Engineer In Residence
If you have other leaks at uncommon areas, a plugged breather would be worth investigating. If you have none, Its likely not worth it. The breather consists of the black box on the valve cover passenger side, and the hose that runs from there to the turbo inlet. This black box is the air oil separator and vent assembly. It serves to prevent positive crankcase pressure, and to also reduce the risk of a runaway event.
 

eranrund

Active member
Forgive me for what might be a dumb question, but would that be visible without taking off the plastic engine cover? (I don't remember how things look like and it's been awhile since I looked inside the engine bay)
 

Nautamaran

2004 140” HRC 2500 (Crewed)
No. The breather is under the plastic cover, opposite the injectors.

You can also use the “dancing oil fill cap” test to roughly gauge blow-by and possible crankcase pressurization.
Carefully loosen the oil fill cap with the engine idling. It may float a bit but it should not be blown away by the pressure.

-dave
 

vanski

If it’s winter, I’m probably skiing..
If the ccpv gasket has failed you’ll see oil seeping from under the injector cover on the passenger side, especially towards the rear. Very common on these older rigs at this point. I just fixed two up this week.. another candidate which could possibly be mistaken as a main seal failing, although less likely, would be a cracked cam cover with the tube at the back previously removed thus oil dripping all over the back of head/block and of course the bell housing area.
 

Midwestdrifter

Engineer In Residence
Also not common, but oil can leak from the head gasket on the rear of the engine.

Torque converter seals can also leak, but its typically easy to tell engine oil from trans fluid, as engine oil is jet black and smells different.
 

vanski

If it’s winter, I’m probably skiing..
Message... lots areas to check for oil leaks.. could be a rear main seal though I guess; if your mechanic has worked on a lot of these T1ns I’m sure they checked all these spots before pointing the finger at the main seal.
 

eranrund

Active member
Sounds like more research is needed on my side to get to the bottom of this... I'll remove the plastic cover and see if I find any hints of oil leaking at the top, and try and clean underneath to make it more obvious where stuff is coming from.
Vanski - I'll reach out via message.
 

forrestfire

New member
I also have a rear main seal leak on my T1N, although it's entirely my fault. I made some amateur mistakes in installing my rebuilt engine by myself and will have to remove the trans for the second time to replace the buggered up seal. I've been keeping an eye on it and its maintained a slight drip for a few thousand miles, as soon as i can piece together a few days off in a row I hope to get to it. Also in the Bay Area but have given up on mechanics here- sprinter shop rates are insane in Santa Cruz and its worth my time and investment to just do it myself, even if it means doing it twice (but not more than three times!)
 

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