I would say it is an easy diagnosis, your cruise amp solder connections need to be resoldered. it is very very common with several MB parts in the W201 and W124 cars. You may get lucky and find a decent one on Ebay or used, but likely not. Most are past their prime and need resoldered. It is a simple operation and can be done with minimal solder experience. The cruise amp is under the pass floor carpet, I think. The W201 is there for sure, i think the W124 is there too. In any case, pull the Cruise amp, rectangular aluminum box with orange plastic end likely. Uncrimp the end and slide the aluminum case off. heat and resolder the connections that go to the pin connection to the curcuit board. Lots of posts on the operation. Just be careful not to spiderweb and solder between the connections as to short them out once it is hooked back up to power. Not too difficult and a fast fix. The intermittent connection of the microscopic cracks the solder has created ate causing the intermittent operation. It is very very likely that the actuator and the switch are just fine, the amp is the culprit 95% of the time.
Have fun. ask if you need more info. I have done three of these resolder tasks. Not hard and everytime it fixed the problem.

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Christopher Henkel
1990 190E 2.6 - Arctic white SOLD
1986 190E-16v - Blauswartze
1993 300CE - SOLD
2003 W208 CLK 320 Cabriolet - Magma Red