I had a related problem on my CLK Cab. Window drops and rises a bit when
opening and closing doors. Drivers's window would drop too much and not
rise. Merc fixed it -- some sort of computer reset.
Have you tried to persuade your local dealer to do it FOC? Four years is
not old and this should not happen.
From your ISP I take it you are in the UK (as I am).
For direct contact replace nospam with schmetterling