All good advise in the above posts, as has been said, service history is very important, have had 6 Merc’s so far and would not consider purchasing one with out the history unless it was a give away price, regardless of what the service history says about the timing chain and guides I would change the chain and upper guides anyway, not expensive for DIY job, the self levelling rear suspension can give problems and can be costly to fix, so if there is any hard thumps / knocks over sharp bumps it will need some money spent, start up and idle ( Idle Control ) also gives problems on these cars, does it start first turn of the key and does it idle smoothly immediately, does the cruse control work, if it works does it surge, the control unit can suffers from the same dry solder joint problems as the idle control unit, the top end ( valve train ) can get a bit rattly on high mileage cars and can burn oil from the valve guides, the guide seals can be replaced without removing the head, another inexpensive DIY job. The transmission can also give problems, does it change smoothly up and down with light or heavy throttle inputs, snatching gears or flaring ( momentary high revs ) between gears at light throttle input are generally signs of ware. Hope I’m not putting you off here, I love my 420SEL and would only part with it for a 560 in equivalent condition, good luck.