Interesting discovery ... the fresh air intake on my 2008 E350 started pumping a rotten egg (hydrogen sulfide) smell. Turns out the fluid in the windshield reservoir had some sort of contamination that started to cook (I did take chemistry in college and remember H2S).

First thought was the air intake filter for the ventilation system - filter was clean and it did not carry the smell.

The windshield washer reservoir sits directly underneath the air intake/filter body - when I popped the cap off and took a whiff I knew I had found the problem.

Carefully removed the tubing to the first nozzle in the hood and used the windshield washer pump to evacuate the reservoir into a bucket. If you need deer repellent, this stuff would probably have worked.

Poured in some distilled water to flush and pumped again. All better now; next trip to MBZ I'll probably get some of their concentrated goo for the reservoir.

Hi dmegeath,

I have a 2003 E500 and I think I may be experiencing the same thing that you did. I popped the cap off the windshield fluid reservoir but didn't smell anything. Does the vehicle have to be running when you do this or does it not matter at all? It really smells when I turn on the A/C or heater!!!

Yes, you would smell a problem when you popped the cap if it was the washer fluid. It sounds like you may have mold or a dead rodent or something of that ilk in your ventilation system. Sorry, I can't suggest any remedies as I'm not at all familiar with the MB air control system.

Two ideas.
1. There is a service note that dealers have addressing some sort of a chemical flush of the air system - possibly addressing mold.
2. Also, different years had filter(s) that should at least be inspected - some had separate particulate and activated charcoal filters.