Full update, for any lingering 98-2000 c280 owners.

At about 230k miles, all three of my mounts were shot. The transmission mount is relatively easy 10 minute job.

The passenger (right) and drivers side (left) mounts were both replaced successfully. I highly recommend purchasing the Mercedes offset 16mm motor mount wrench, since access to the top bolts is a bit tricky from above on both mounts (the exhaust manifold sits directly over them).

Glenmore's approach to the drivers side mount worked perfectly, although the fit was tight. As I worked the old mount out and the new one in, moving the tire slightly back and forth allowed enough room to pop it through. I was working alone, and having the steering wheel unlocked with the battery disconnected made it an easy job to do from underneath.

I spent several hours working on the passenger side mount, since the alternator is a pain to free and replace (though much easier once the bushings are worked forward). The drivers side only took about an hour once I tried this approach. All told, it was pretty easy, and less work than the ac compressor approach. I had spent a few hours trying to work it past the unhooked ac compressor on a previous night, and it wasn't working.

Do one mount at a time, and it while it isn't an easy DIY, it's pretty doable. I used Lemforder, and definitely second the advice to avoid cheap parts. You really don't want to be doing this job again any time soon. I've heard horror stories of cheaper mounts giving out after 20-30k miles.