A500 strength over the years ?

OK A500 techs were the earlier (1988-89) A500 weaker units/ that the later (1993-95) units ? Where there "better years of units that might have more clutch discs / or other improved parts ? I'm only going to look for the 42RH units/ no electronics!!
Buy the way, whats the going rate for a used working/non working A500 "core transmission" going these days ?