If you snooze - you lose.

That 300SD sounded terrific.... the trade-in reason was ligitimate... little old lady cars are generally well-maintained.... and you knew the previous owner

Heck, the dealer probably would have taken $1600 .... if you fanned the cash in his face

Now you are looking at 420SEL?? You gotta be crazy! Look for blown headgasket (aluminum head/ iron block).... also lotsa nutty gadgets and gizmos with millions of vacuum lines.