You have the right idea,get an independent mercedes expert to service your car and before you approach them , Ask other customers about them. I am of the old school where I appreciate my customers so I actually get to pick and choose them. If i don't get on with someone,they are asked to go to another place . It makes life easier for both of us and their cars are always running properly and at a price we are both happy with.

A conscientious mechanic will do the mercedes Service properly and go over the car according to the mileage . The steps are outlined in the owners handbooks and list as 'service A B or C etc .' An A service being just a oil change and quick check of fluid levels with a E service being a replacement of all worn rubbers etc etc including checking door seals as it happens .
As a general rule all rubber hoses should be changed every 7 years although I have worked on plenty of elderly mercedes With 40 year old radiator hoses still giving top service.
You have done your brakes but did they replace the hoses as an example?.
By doing a proper book service the mechanic can rest assured there qwill be no knock backs and the customer can drive the car knowing that only a really unlucky event will cause a problem.
The mechanic wins because he makes more money,the owner wins because service is really cheap maintenance and a lot cheaper than a new engine or trans because they didn't bother to mention the old heater hoses.