the w210s have a weakness in the shifter unit and i believe the common ailment
involves the shifter bushing. generally, the light is out rather than staying on.
but since it is a known weakness...and it impacts the reverse light switch, it
may be a good idea to check the bushing anyway while you're trying to isolate
the problem.

i also seem to recall that the shifting module (electronic) is easier to repair with
the 96-99 models vs the 00-02 (which do not easily allow dismantling)

__________________
-- raymond~
47º 34'N 122º 18'W