Honestly, you would probably come out ahead selling the car AS-IS, and saving the money on repairs. That is probably 2K worth of work you listed at a reputable shop. Sell it before any major, catastrophic repairs are needed.
You can get a similar vintage E-Class (W210 96-up) or (W124 95-down) with half the mileage. It is a buyers market. 3-4K tops will get you a very very nice E-Class. Going to an E will make you seriously doubt ever going back to any C-Class! At 275K, that car is pretty well used up. Things will start breaking/failing at an accelerated rate as you get closer to 300K.
Yes, you could fix it and get another 50K out of it. But it's running on borrowed time IMO.
