Thank your for quick response.

I did a quick search and I saw the issues about the 350 SDL, but my Wife's sister's best friends brother knows a guy that ran into a diesel mechanic once at a boat show in North Dakota and he said that certain 350 SDL's can be good cars. He was told the following:
1. If the motor was replaced by Mercedes under warranty, then it has the better parts so it would be ok.
2. As long as the car has had regular oil changes at 1,500 miles it should be ok
3. You can do a check by taking a screwdriver and putting one end up to the valve cover and the other end in your ear and have somebody rev it up to 6,000 rpm you can here if it sounds like the motor will break.

I appreciate your help gentlemen.