124 shifter bushing replacement
I have an older body style (124) - but the bushing replacement made a big difference! I think the two bushings cost me maybe $1.50. Probably the biggest ROI you'll get in a Mercedes part replacement outside of a blown fuse. Installing them is very intuitive. One at the transmission, one at the bottom of the shifter.
The only trick is getting them pressed in place. The one at the shifter (near the rear of the car) is toughest because you're laying on your back and reaching around the drive shaft. The other takes more disassembly, but it is done on the bench. I've been blessed with big, lanky, piano-player fingers and an 11" set of needle-nose pliers. But I'd say most important is patience.
FYI: I had my car to a transmission shop, and asked if he would mind doing it for me. He said "No problem. Give me the bushings and I'll charge you half-hour labor - $30". I figured he had experience with this repair. I was wrong.
He called me back moaning about how it took 4 hours to get just one in (the transmission one, which is the easy one because you do it on the workbench), and that he'd have to charge me at least two hours more to get the 2nd one in - and that there was no way I'd be able to do it myself. He had me scared - but I told him not to finish the job and thanks for trying. I brought the car home, and spent more time jacking-up the car in my driveway than actually installing the other bushing.
That said, yours may be more challenging if they are very hard to reach.