First question should always be "Show me the service records."

Then I would say look for one with about 100K miles that has records for some of the predicable biggies. Those would include headgasket, A/C compressor, radiator, etc. etc. There are a bunch of 100K to 120K predictables and it's better to have those already done.

Also look at the coolant. If it's green instead of light orange, then I would not buy. Incorrect coolant equals internal corrosion.

I had a '90 300E bought at 100K sold at 175K. I have a '92 Factory Sportline that I bought at 113K and currently it's at 244K. Engine still running strong with no valve job yet. A long list of repairs. Some necessary, some upgrade, some just pure anal.

I would pay a whole lot of attention to paint. This is very expensive to remedy. Also find the number stickers for the fenders, doors etc. They should all match. Look closely for signs of a wreck or body work.

When you find the one you want, and have done your best analysis, then take the car to a independent MB shop and pay them to do a PPI (Pre-Purchase Inspection).

Steve
'97 S320 114K
'92 300E Sportline 244K