A caution to DIY Sprinter campervan owners (and anyone with covered lower walls). Check for leaks!

While running some wiring I removed a wall panel and discovered that the area inside my rocker panel was damp and mildewy. On further investigation, I discovered that all the lower wall panels had moisture settling inside. Even though the walls had only been covered for three months, I was starting to get mildew inside my walls!

Some quick internet research (thank you Sprinter Forum!), and a garden hose test I found that the water was leaking in from the plastic trim clips. According to the Sprinter Forum, this is a common issue dating back to the 2006 and earlier Sprinter vans. This ridiculous (and unresolved) quality control problem is undoubtedly contributing to premature rust in tons of Sprinters, as well as mildew and mold inside covered walls.

My original idea was to apply caulk from the inside, around the trim clips. Sealing leaks from the inside is not the ideal solution. In general, it’s better to keep water coming in from outside. Like many good DIY projects, this one quickly escalated out of control. I started pulling the plastic wall panels using my cheapo set of Harbor Freight trim panel removers. I quickly realized that I had a nearly 100% failure rate on all the panel clips. They all had dirt built up under the exterior flange, indicating that water and dirt readily flowed behind them (resulting in leaks into the cabin space).

After removing all the panel clips (with needle nose pliers and a screwdriver), I used a gutter and flashing caulk I had leftover from a home project. There are a lot of great caulking products. I used one that is not latex (water soluble) and could be applied on wet surfaces. I applied a daub of it around the hole, reinstalled the clip, and rotated 360 degrees to get even distribution of the caulk.

I finished one side of the van in about an hour.

Caulking around the holes is not an ideal solution to a ridiculous problem. To say that I am frustrated that Mercedes would sell a $40K+ vehicle with a known leakage issue into the passenger cabin because of $0.02 panel clips doesn’t really seem to express my feelings. This is shameful. I am guessing that there are tons of Sprinters with premature rust problems because of this. Any leakage into a covered space (any sprinter with covered lower walls) has no way to evaporate. Moisture inside covered walls leads to rust from the inside out! In addition to rust, mold and mildew in the cabin space is also a concern, particularly for anyone with insulated walls.

My solution to the leak problem may create other problems if I need to replace a trim panel, but at least it should keep water out of my walls.

A panel clip with a rubber gasket and more secure mounting would fix this issue permanently. A permanent fix for this issue would cost Mercedes a few more cents per fastener and a few extra minutes of assembly time. Enormously frustrating.

Note that I am in Northern California (not a rainy or wet climate). I bought my used Sprinter in Palm Springs, CA (think desert, 100F+ days, and cactus) in July 2016 (in a drought). My Sprinter had likely only seen rain a couple of times in its first two years. I can’t imagine what Sprinters in rainy areas look like.

Tools I used

Trim pullers ( from Harbor Freight)

Needle nose pliers

Flat head screwdriver

Rags to clean up the hole and excess caulk

Caulking gun

Caulk (I used a flashing and gutter caulk that could be applied wet)

Links and other information

I found the Sprinter Forum invaluable in a quick resolution to this issue. I was able to confirm the issue, and confirm the leak source (by spraying side of the van with a garden hose) in a few minutes. Here is the main thread I found on leaking trim panels. A huge thank you to those on the forum who documented this issue as well!

Please leave any comments below on the blog. Others can benefit from your experience and solutions! Thanks!