First I'd like to say as a presumed non-native speaker, your english is perfect.

W140's are notorious for leaking a/c evaporators, so that might be one thing to check out.

Regarding your alleged missing problem, check to see if you are running the proper non-resistor, copper core plugs. The resistance in this ignition system is in the spark plug boot, so running resistor plugs is not recommended.

Also check the condition of your distributor cap and rotor.

__________________
Paul S.

2001 E430, Bourdeaux Red, Oyster interior.
79,200 miles.

1973 280SE 4.5, 170,000 miles. 568 Signal Red, Black MB Tex. "The Red Baron".