It is a very important part in the handling of the car, and is a pretty inexpensive part to replace. Do a search under "Thrust Arm" "Control Arm" "Floating 300E" etc. Lots of descriptions of symptoms, part #s, prices (about $35 each), etc. Most 300Es seem to need them before 100,000 miles. I just did mine at 77k miles. The tech said they were worn, but still within limits for most drivers, and were good for another 20-30 k miles. I had him do them anyway, and I could feel the difference (Almost all of my suspension is new, and I could still feel a difference from just these arms!).
2003 Firemist Red/grey leather SL 500
2015 Palladium Silver/black mbtex GLK 350
1987 Smoke Silver/burgundy mbtex 300E Sportline (SOLD)
Click to see 87 300E