Update. All w140s had new refregerant and the black 1993 300sd I purchased had everything AC part under the sun replaced during multiple visits (including the evaporator.)
I never got to see the 1995 I wanted to; it sold for the new asking price of $9995 with 133k and a carfax showing the evaporator repaired back some time. I basically payed dealer retail for mine minus about $700 for a new front bumper (151k on car). The 1994 I saw was scary. Never been in a wreck and looked nice, but quite a bit of rust, heavy salt damage on rims, and much to my chagrin, despite having the 22 01 cylinder head, ran poorly enough to scare me off. It felt like a neglected car. I finally got to see a 1995 locally that was amazing condition. It had been an old lady car and was all original with nice, nice leather. The guy wanted $2000 over retail and I found a busted rear window regulator and an issue with the dash and steering wheel vibrating at idle that must have been engine mounts. The car looked like it was 2 years old (156k on the clock) and I suspect the mount issue may have developed from being in storage the last four years with only really big trips once in a while. It has to be the best cosmetic condition w140 diesel in existance and I offered $11,000 (10k first), but owner would only come off the price $500 despite my finding $2k in repairs. My 1993 felt like new which could not be said about the other two cars and has a good enough paint and interior that it should be exceptionally nice. All cars I test drove had both power headrests broken (people need to read the owners manaul).

Despite their reputation I would say the market is strong for the w140 diesel since it is the most luxurious diesel available (not counting the return of the S class diesel in the USA this year; $108k well equipped I saw on the sticker.) The other w140s by in large are worth much less. I just saw a nice 1994 s420 (which would be the gasser I would want) on ebay with 113k miles and it had been reduced to $6300 (nice looking one in video.) I'll be calling my insurance money to squeeze some more dinero from them given the difficulty acquiring the diesel and the high price. The tables have turned from when I purchased 10.5 years ago.

The car I purchased had a good repair history and was a case study on how a w140 diesel can get you. Within the first 3 months the second owner had the car, he had rod bending oil consumption and then right after reparing that the evaporator went. Lucklily he had gotten a three year warranty from the dealer that defrayed $3500 of the expense and he got a junk yard engine for $2k so was only out about $4k from this double debacle plus the cost of the policy. Lots of good suspension work and other things done on the car so I think it is good. He had let the aforementioned bumper go and a litany of minor things which I am salvaging myself (antenna, headrests, powerclosing, trunk not working right at all with some leaking and minor rust behind lining, infrared issue-turned out to be button in key, center console latch, and soft shock on glove compartment). I've repaired most of this with some pulls from the old one and the only remaining issues are vacuum/engine stuff. My take is they were just getting rid of the car because engine wasn't running quite right and all of these minor things were diminishing the owner experience. I've spent $0 and have the thing running even better (amazing shifting and in town acceleration.) I'll be posting shortly on the vacuum stuff as it has me really stumped. As is at the moment it feels like new on the road which is an amazing experience I never quite got from mine. With heated seats, moonroof, and ASD this thing probably went for $80,000 new and I can almost see why someone would have coughed up this kind of money for one of these. I am in restoration/perfection mode with this car and rather enjoying myself. I'll still always lust after the local cream puff which was blue black, but my bank acccount is about $5000 ahead and probably more in the long run since I know my current car was not let go.

I hope this helps anyone else looking at these. I had an overwhelming feeling on pulling in to town with the new car of now I've got two of these, what on earth have I done, but that has passed onto enjoying perfecting the operation of the new one. The car should depreciate about $200 a year from here on about based on kb difference between 93 and 92s. Don't be scared diesel experts, buy one! These cars need a good care taker who can do much of their own work.