New Passenger van - Water leak into passenger side B-column

I am in the middle of installing a cabin heater in my brand new passenger van. To avoid any major drilling through the floor, I was going to route the exhaust through an existing opening in the passenger side b-column. After I removed the interior trim from the B-column, I noticed that water was puddled up inside on top of a Styrofoam pad that is sitting in the middle of the column. There seems to be a small leak somewhere from the roof into the column. I was wondering if anyone else has seen this type of issue before.
See the attached picture:The foam pad, on which the water collects, sits right under the larger rectangular opening in the column.

Most likely one or more of the plugs in the roof where the roof track bolts would be, is/has failed or the gaskets/washers around the roof track bolts themselves seems a good 1st place to look.

Thanks for the feedback ! Yes, this was the 1st possible root cause that came to my mind, too. However the last (most forward) bolt of the rail sits about a foot behind the B-column and further inward. In any case, I have painted the bolts with three coatings of rustolium enamel yesterday. Still waiting for the paint to dry completely before I do my next test.

Just want to report back that the leak appears to be fixed.
Aside from painting over the roof rail bolts I did one more thing. I took out all screws of the sliding door hardware that is mounted to the b-column and re-installed them with blue locktite.
Not sure which of the two fixed the issue. I am glad I caught this now before any onset of rust.

Tri polymer sealant like Henry 212, or Geocel 2300, both clear is a good choice too. I used it on my sliding door moulding clips. Can be used on ether side, pre or post installation. No acetate's like silicone.