I had the same problems on my 82 240d.
I took the GP relay apart and found water in it. There are 4 small screws that you remove on the top of the relay & then the actual "relay" (circuit board thing-a-ma-dealie) comes out. In my case the water had corroded the solder on the circuit board - so I just soldered in a new wire to "jump" the corroded section.

Just a thought.

Aivars