Working on Same Problem
The rear subframe mounts on my wife's '92 300e completely failed and I'm in the process of replacing them right now. It seems that the big washer below both of the forward mounts corroded away and the rubber inside of the mounts tore away. The rear axle was "jumping" under hard braking.
Anyway, Fastlane's kit for the front subframe mounts is about $80 and includes both front mounts. I went to the dealer and they wanted $135 each and they only had one in stock so I decided to order the parts from Fastlane.
I took one on the mounts out today and it did not go very smooth. I tried making my own puller out of steel plates and treaded rod but the inside of the old mount was so torn and corroded I couldn't get a grip on the bottom edge of the old mount to pull it out. I ended up mutilating the mount and plan to do the same on the other side. I drove two cold chisels under the top flange until the inner shell of the mount popped out, then to remove the outer shell I drove a chisel vertically along the outer edge to deform it. This, in effect reduces the diameter and it comes out easily. I spend 1 1/2 hours trying various means to remove the first mount. We'll see how the second one goes.