I recently bought the above car and it has some issues:
1. Fuel Gauge-When the tank is full the needle moves very slowly as the tank empties. When the needle gets to 3/4 of a tank, the needle jerks back and forth for a second, then plummets to empty and the reserve light comes on. After driving 100 miles, yesterday before the needle hit the 3/4 mark, I started loosing power and the engine died. I was able to restart it but the car would only go 40 MPH and then it died again. I was able to get it to a gas station and refueled. It started right up and ran fine until I got it home, about 15 miles. My guess is the fuel sender?
2. Car has no power, like the turbo is not working. I have to floor the car to climb or pass on a long hill on the highway, in 100 miles it only kicked down one time, I had to shift the car into 3rd to climb a long steep hill. The trap oxidizer has been removed and a new exhaust sytem was intalled by the previous owner.
3. Front seat springs are shot. Can they be repaired or can new ones be had?
I have a copy of the W124 Owners Bible coming. Hopefully, some info/pictures will help.
Thanks

 

I have the same car. I think the first place to start is to replace both fuel filters. There is a one on the top of the engine on the front drivers side(looks like a spin on oil filter) and a clear plastic one by the injector pump that is between 2 rubber fuel lines

The seat springs wear out. I found some foam seat spring supports on ebay.

The fuel gauge sounds like the fuel sending unit in the tank is bad

That is all I can help you with for now. Mine is still a work in progress and dont have much time to put into it