water leak on both the C280 and E320 - what the hell?
 

After heavy rains my driver side floor board is soaked. I am not talking hurricane force rain but slow and steady for hours.

96 C280 had the problem when I was on an incline but seems dry today after several hours. Parked on level surface.

01 E320 sat no more than two or three hours and passenger side behind driver has a few gallons of water sitting.

2X on different cars - is this a known problem with MB?

no, that's not a know problem with MB...as a matter of fact I don't think it's a known problem with any marque.....I never heard of that one..ever...

Sounds like you need to check all of your drain passages and make sure they're not jammed up with dirt, leaves, acorns, etc.....

Park under trees much?

We had that problem on our 1997 C230. Bottom line was that pieces of leaves (despite my best effort) had worked their way in to the water ducts. We had standing water inside one day so I knew I had a problem. After reading on this forum, I opened all four doors and ran a hose full on (without a nozzle) against the windshield. I saw where junk was trying to flow out and used a bent shisqbob to dig out the crud. There is also a duct in the engine compartment down low below the windshield on the right side. I bet that is where your major block is. Use the water pressure flowing down from the windshield to see where it is blocked. It should be gushing out the engine compartment hole and flowing pretty quickly out the holes that are in the door jam area. When the water flows freely, you're done. Good luck.