I am looking to buy a 420/500/560 SEL from '90 or '91. I am wondering, what are some known issues and thinks to look for on those models? It seems that many do not come with heated seats. Is is realistic (how expensive) to have seat heaters installed? Why do the prices fluctuate wildly (even within those of the same mileage it seems)? Anyone bought one from ebay? How did that work for you?

Thank you for your help and guidance.