Excellent data points! If I may summarize what I hear:
1. Ownership experiences with the M104 have been good/great.
2. There are problems, but they are well documented and solvable.
3. Find one that has had the 'typical' failures corrected.
4. A warranty may be a very useful to have.
Given these points, I am leaning heavily towards a 94/95 wagon,
althought I suppose since the 93 had the M104 as well, it could be a candidate for consideration. I greatly prefer the styling changes to the 94/95 models. Besides, there weren't all that many 93 wagons sold (<1000), making them tougher to find, but potentially cheaper, as I suppose many people would prefer the later cosmetics (headlights, especially).
I have searched the MBUSA starmark inventory database and find that there are several starmarked examples of the 94/95 e320 wagon available for less than $20k or so, within a days' drive from where I live (Cincinnati, OH).
I really appreciate all the feedback, and will continue to monitor this thread. THANK YOU!