Originally Posted by +fireamx

I've checked under the rubber gasket of my doors several times since Andrew first made his post back in December. Each time I found the area to be damp, with alot of soap residue that had a orangish tint to it but I never noticed any actual rust. So I'd just wipe it as clean as I could, spray some silicone on it, and replace the rubber gasket.
Saturday was such a bright sunny day, I pulled my car out of the garage (facing north) and open the doors and pulled down the rubber gaskets. Since the bright autumn sun is sitting lower in the Southern sky now, it totally lit up the entire problem area like I've never seen it before.
After I cleaned off all the soap residue with a 1/2" wide nylon paint brush and some soap and water, I noticed what looked like very slight bubbles under the paint on the vertical section or back side of the through that holds the rubber gasket. They almost looked like "spot welds" as they were lined up directly behind the 7 small "cut outs" on the outer lip of the trough.
I then took a very small flat edge screwdriver and pushed on one of the bubbles, and sure enough, the paint chipped right off. I proceeded to use the screwdriver like a paint scraper and broke open all seven bubbles. Fortunately I was able to scrape the surface rust off, and the metal still seemed to be smooth with no perforation anywhere.
I then cleaned it the best I could, and even used spray-on brake cleaner (hopefully to remove any silicone that was still on the surface) and I coated the bare metal with two coats of Rustoleum "Rust Reformulator". It's suppose to stop rust and make the area safe to paint over.
I haven't decided what kind of paint I'm going to use to seal the area, and I'm still thinking of drilling extra drain holes through the bottom of the entire length of the trough.

The reason I'm bringing this up, is because you may have to look very closely to actually see the bubbles, or any tell tale signs or the start of corrosion. Even on my white car, it was only the bright sun light that enabled me to see the bubbles, when I never saw them before.
Every one of these cars (if they are ever introduced to moister) are going to eventually have this problem. You can bank on it, it's a sure thing.
The very first thing I would do if I was buying a brand new one, or a used one, would be to take it home and address this problem area immediately.
The only way to prevent it from happening is to seal it with some sort of epoxy, or urethane paint (like Por 15, or the Rust Bullet) before it starts, or after you make the inevitable repair.
You can be sure that most serious car enthusiast (aka potential buyers) in the future are going to be well aware of this "Benz Cancer" curse that our cars inadvertently wound up with thanks to their "DNA". So waste no time preventing it from starting on the new cars, or returning on the used ones.