Using 2phast's (
www.2phast.com) instructions from his shifter swap on the 500e ; I swapped a c280 (w202) shift knob & shifting shaft into my w124 this afternoon, and it was pretty quick and painless! I'm glad I grabbed the shaft though, (almost didn't) and here's why. You totally
need the w202's shaft and knob because the w124's have a nut to lock the shaft / screw in configuration. The stock w202 (c class) shaft + shifter aren't like this, as the shift knob comes of easily (twist the bottom piece, then pull it off of the shaft) and it's one solid piece, without a lock nut. The good news is - it fits perfectly into the w124, using your old clips / hardware from the w124's stock shifter. Mine's brown which doesn't really match my interior - it's okay with the wood though. I'll eventually change the knob, but the shaft is the important part

errr yeah.
You just use the shaft from the w202 in place of your stock w124 shaft, pop on your knob and you're done. The W202 shaft part # is [ A2022670401 ] & is a OEM replacement for the W124 and W201 and provides you a shorter and thicker shaft which uses the new type of shift knobs found in the W202,w203,w140 as well as others....
W202 on the left, W124 stock shifter on the right
here's a pic of the shaft parts :