Eskimo,

i own a 85 300SD with 200,000+++ miles on it. When the A/C went on the previous owner it was a leak in the lines. The PO decided to convert the A/C to R134 and it has not quit since. Now, one area that might be of concern to you and that is a problem on these W126 is the climate control module in the dash. They seem to crap out. My suggestion is, when you get there see if the compressor turns when you engage the A/C. If the A/C engages and runs, then you know there are no leaks in the system and its just the A/C control module. But! This is not an inexpensive part...you might be looking at about $200.00. Ebay usually has used ones for cheaper but I's Beware of those!! The 300SD is a great car. The engince, as you probably have already read around here is litterally bomb-proof. So if the A/C is the only thing wrong with it....Go for it!