Sorry to hear about all your problems. To make it worse, those problems appear to be occuring on a car with low mileage (48K km is not what I would call high on the mileage scale).
As to cost of the recommended mileage checkups, I had my 320 in for a 90,000 mile checkup about 2 months ago. The total cost for that was around $750 USD. I was very satistified with the work they did.
Can you ask the shop manager to tell you what the thickness of your brake disks are? I have the complete set of Service Manuals for the Series 124. (I have always worked on my own cars, but with the MB I pretty much let the dealer do the work because the car is simply too complicated and I can't afford to buy a second set of tools--plus the special tools that are sometimes required. However, I find the manuals useful to both doublecheck what the service folks tell me AND to understand the car's systems. I am an engineer so I enjoy this type of reading).
- Jon E320 210.055
77 Mustang 307,000 mi
63 T-Bird [fully restored]