I truly understand your frustrations. I've done this job myself on my '84.

I did my heater core replacement. What a major pain, but once done, that working heater is more wonderful, knowing that I did it myself, and saved about $900 labor.

While I had the heater box out of the car, I cleaned the insides of it thoroughly, and the sealing surfaces, too. Replaced 2 of the little vacuum actuators... the green one on top, and one of the pink ones, as they were not holding vacuum more than a couple of seconds.

No heat? I discovered that the slider switches in the heater control module were coated with years of cigarette smoke and road filth. I cleaned them all with electric contact cleaner, and resoldered the connections on the PC board inside the heater control box, and replaced every electrolytic capacitor on this module... they dry out and go bad after 20-25 years in a hot car!! My whole system came back to life after this work was finished.... No A/C, though, as a previous owner removed the compressor and cut the refrigerant lines out.

I've got an electronics repair background, and know how to troubleshoot. Dont just assume that something is wrong. Throwing parts at it is something I did at first, but stopped, after several times of seeing the problem was no different than before, other than my wallet being a tad lighter.

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My first Mercedes Benz. 4/6/07.

1984 190E (201 024) 2.3L four.