Replacing guide rod mounts is tedious in a rust free car. I can only imagine the headache in a car that's seen salt.

If the looseness is confined to the rear mount then the trickiest part is moving the wheel forward to get the new mount in place. You can use a come-along to pull the lower control arm forward or deflate the tire and use a jack between the wheel and fender. Spread the load along the fender liner so you don't damage anything. It doesn't take much force to move the wheel forward with the guide rod mount loose.

If there's looseness in the front attachment, the sring has to come off to remove the lower perch to get to the front bushings. Use only a spring compressor designed for MBs.

Everything to be said about shock selection has been said :/

Sixto
93 300SE 3.0