This was a good writeup and I just wanted to add to it with my experience on my 1993 190E 2.3L.

I replaced my mounts with some mounts from the partsbin. I got worried when I saw they were "Made in China", but went ahead and installed them anyway. Things were fine for a couple of months, then the rough idle returned, maybe even worse than before. After reading lots of posts, I decided to spend $180 for the OEM Mercedes mounts.

While they looked very similar, I installed them and now the idle is totally smooth, just like new. I saw some evidence of leakage on the mounts that were only 3 months old.

When it comes to motor mounts, only go to the dealer.