ullrich,
This may be a long shot, but here is what I did on my 81 300TDT:

This car was in an accident and the drivers side headlight assembly was totally crunched.

After replacing the assembly, I plugged the lights back in and found that the turn signal would not blink-but it came on- or sometimes it did not come on at all. (It blinked real fast b4 I replaced it...)

So I check the connections at the turn signal bulb holder and everything *looks* OK. I try another bulb, nothing. I then try to open the little box at the end of the plug to see the actual connections (If this is confusing, I will post pics) and one of the wires had come loose. Re-soldered the connections and BINGO good as new.

It's worth a shot.

__________________
Current: '91 300TE 4MATIC 317k and climbing...
Former:
'81 300TD Wagon 168K "Tank"
'83 240D 216K 4spd manual "Da Bear" (aka best car ever)

"Never sweat the petty things...
and never pet the sweaty things."