I never owned a Mercedes.
Mom and dad had a diesel model before diesel was cool. They fought with the dealership on a hard shifting condition within the auto trans. Never got resolved. Convinced mom later to sell it and move on.
I myself have owned and maintained two Audi's. A 5000 and a 100
When the fuel pump went out of the 100 it was $600 from the dealership, $300 from Napa. When I wanted to change the timing belt I needed a very specific harmonic balancer puller thats not available from any parts store. I sold the last Audi in 2000 and never looked back since while driving American trucks.
The lesson I learned was that parts, service and the special tools needed are exspensive and hard to come by. Sure, German cars are of decent quality but you are going to need deep pockets.