2001 Mercedes Benz C240W - mileage 33,883

I recently had motor mounts and thrust arm bushings replaced on my 2001 C2240W. Prior I have had a mass air flow sensor, fuel sensor and a water pump leak and 2 socket seals leaking.I have spent a total of $3,000.00 on this car since I purchased it in 5/2001. I feel this amount is excessive. The dealership told me that seals and gaskets are lubricated with driving and my low mileage could be the cause of problems that I am starting to have. I am a single middle aged female. Are they taking advantage of me? I dont think they are telling the truth. I drive the car every day, I just dont drive far which should take care of the lubrication part that they say. Would I have this kind of problem on any vehicle or have I bought a lemon?