300SD clunking noise in park

[willrev]

Have a 1982 300SD in excellent condition. My mechanic just adjusted the valves. Engine is running much better. It does not do the shimmy shake while in drive and stopped at a traffic light any more. Just got home from a 200 mile trip and when I pulled into the driveway and put it in park it started to shake and make a knocking sound. I put it back in drive and it just purred and no shaking. Back to park and the shake started again. Mechanic said the motor mounts have never been changed and were compressed. It has 250k miles. I am the second owner. The first owner had the car serviced for 22years by the same mechanic. Should I replace the engine mounts? Also car is sitting lower in rear than front end. Should I Relace the differential rubber mount as the **************.com website suggested or should I replace the rear coil springs and if so, should I go back with a heavy duty spring and which one? Thanks.