Forget about Mercedes taking responsibility for it, that would set a precedent they will simply not go down that road.
My 1995 E320 was garage kept and detailed yearly for the first 10 years of its life (besides the regular washing) and had rust issues in 2005 when I bought it. Now in the past 5 years it is simply rusting from the inside out.....everywhere. Doors, antenna mount hole, wheel wells, the entire frame rails, engine compartment (ahead of the shock mounts). I pulled at some loose rusty metal and ended up with a 6" hole in the engine compartment on both sides by the wheel wells.
At this point with about 220k miles on the car and having performed almost all the typical repairs these cars are known for, I am just going to drive it till it dies.