The only way to enjoy a 35 year old car is to maintain it. If the seats, turbo , AC, and suspension need work, fix them. Don't complain that neglect of these problems and probably others make this car less than a joy to drive. When you have an older MB, the only way to make it a joy to drive is to keep it in good repair and to fix its major problems. If you can't do that, buy a newer car.

I have justified major expenses in fixing my AC (compressor and evaporator) with the rationale that an MB without air conditioning is not really an MB. Either I pay for it or get rid of the car.

My view is that it is generally cheaper to fix the problems on a car you already own than to buy a newer car. The problem comes when you let several major problems build up, and it looks like you are better off by buying a newer car. The problem you have with the newer car is that you don't know where it has been neglected and what repairs it will need.