rear roof cap leak

ApresVanagon · 03-01-2021, 10:51 AM

We have a new to us 2017 SMB Sprinter with a penthouse. We seem to have a leak through the rear roof cap (show in picture--the one closer to the penthouse). We noticed because water was leaking into and then through the rear interior light (shown in picture). Anyone else encounter this issue? My temporary fix helped but now I believe I should start over with a new cap and sikaflex 291? Any ideas where I could get a new cap for that hole? I doubt that will come out in one piece!
As an aside ...it seems that there is considerable condensation in that cavity in addition to the leak. Thanks for your time and thoughts!

Fitz · 03-01-2021, 11:27 AM

Did the cap come stock with the van? I'm thinking MB put it there for you and if so, that's where I'd go next.

86Scotty · 03-01-2021, 05:38 PM

I typed a response to this but it seems to have never gotten sent. You can't tell anything about possible condensation until you get the hole properly sealed. I wouldn't remove/replace, I'd just put Sikaflex around it and try it. Then, if that doesn't work consider going deeper.

ApresVanagon · 03-02-2021, 02:22 PM

Thanks for your feedback/input --that makes sense. Do you use Sikaflex 291? Or is there another sikaflex product that you prefer?

86Scotty · 03-02-2021, 03:16 PM

I don't know but someone here will. I have yet to use Sikaflex (any of them) on a project because I have a shop full of older school stuff I haven't run out of. I only heard of Sikaflex in the last few years but everybody seems to be using it for things like this these days.

Someone will chime in and know. If you don't have an answer in a day or two remind me and I'll give you a few to choose from.

marret · 03-02-2021, 03:30 PM

I was reading on the Wanderlodge Owners Group forum about filling bolt/screw holes.

Recommendation was as follows: Sikaflex 221 holds its shape better for using under screws and stuff like that. If you need a little flow for self-leveling Sikaflex 715 is better for that. Sikaflex sticks better, lasts longer, doesn't have any silicone in it, and it stays flexible.

SteveTOaks · 03-03-2021, 12:01 PM

This issue was discussed several years ago here https://www.sportsmobileforum.com/fo...use-16458.html

ApresVanagon · 03-03-2021, 02:27 PM

Thanks Steve -- I attempted to resurrect that thread but I guess it didn't work... I saw your response there and solution there. My van is currently at Mercedes dealership so I'll see what they say. I asked them for a new cap at the very least...

Charliesmom · 03-04-2021, 10:44 AM

Ford Transits also have these roof caps (22 on my HR 148 WB). The holes are threaded and are covered with plastic plugs, similar to the MB. They are useful to install racks, solar panels, etc. The issue and its solutions have also been discussed in the Ford Transit Forum. Most owners are doing preventative measures over any unused holes, as they can potentially leak if the paint cracks around them. I plan to use Dicor leveling sealant on my roof.

ApresVanagon · 03-04-2021, 01:59 PM

Thanks Charliesmom...that Dicor product sounds interesting-- I hadn't heard about that--UV stabilized and flexible sounds very appropriate for a roof application. I'll search the ford transit forum for more info...