I just had the pleasure of replacing a lower ball joint on my daughter's '87 300E last weekend.

DIY? yes / easy? not really

You pretty much have to strip that corner to get to the joint. I supported the control arm (& sping!) with a jack and placed a jack stand just inside the ball joint for support. Hammered the old joint out... had to keep going to a bigger hammer!! It was very stubborn coming out, then suddenly popped out. Pressed the new one in with a C-clamp-type press borrowed from Autozone (FREE).