This past spring there was a really nice '93 500SEL for sale at the MB dealership - 71,000 miles, black, black and they wanted $20,000 for it .

I think a lot of the w140s that are crap were original lease cars that were bought by second owners (after the original lease expired) who did not take care of them. They have paid them off and are trading them in for something else now - usually not MB - which is why they also do not have records with them. When something expensive broke that was not detrimental to the actual running of the car they just let it go because, after all, they already had a fairly high car payment to deal with.
I am also really surprised that the MB dealership here does not keep records, tools for locking lug nuts, sheepskin seat covers, etc. that come with the cars when traded. I don't know if this is because they don't know any better or what.
When I found my 420SEL I was actually looking for a W140. I am glad now that I got the 420SEL given my current financial state. I will get a W140 when I am out from under credit card payments, car payment, etc. and can actually come up with a decent size down payment and some $$$ in reserve just in case.