GREAT HELP! Thanks so much. Just wanted to note that these instructions apply to the W210 E300 and E420 and probably NO OTHER W210 models (however they could be adapted to be helpful). The E420/E300 have TWO inlets and TWO outlets for some reason, and the rest of the W210 lineup only has one inlet and two outlets (or vice versa on the inlets/outlets).
I actually ended up rehabbing my valve using parts from a valve off an E320 so was able to compare them side by side. Basically, the E420/E300 valve has an extra layer... which is pretty much this section from previous photos...
I believe the biggest issue with my valve was the degraded O ring... this part...
The center section from that seal was all gummed up inside the valve. Probably would have had a pretty good chance of the valve working right just by cleaning up/trimming the center section as outlined in the instructions (and also removing the tattered bits, of course). I was able to scavenge a similar seal off the surplus E320 valve I found.
I also used two rubber washers that were in good shape from my extra valve. I don't think it had the four washers like the E420/E300 valve with the extra layer, but that was OK as two of the washers from my orig valve were in good shape.