Here is a data point.

Last week, eBay had an auction of a 1992 300D with 313kmi. See the discussion at

http://www.peachparts.com/shopforum/showthread.php?threadid=28777&highlight=300d+selfleveling

It is still active and the price is $4,500 (met the reserve already)

Here is the auction link

http://cgi.ebay.com/ebaymotors/aw-cgi/eBayISAPI.dll?ViewItem&item=599784311