Trond:

I can't help you with your problem, unfortunately, but I just had the A/C evaporator and the heater core replaced at a shop on my 1992 SL500. The consensus seemed to be that the hardest part of the job was removing the dash to access the heater box and A/C evaporator.

How hard was removing the dash? Were you all the way down to the A/C evaporator?