Mercedes: buying an old mercedes, mercedes diesel, old mercedes

Question
First, thank you for taking the time to answer my questions. I need to buy a car and have been thinking about buying an old Mercedes diesel. I am not really concnered about mileage because they seem to last forever.

I had a few questions about it
1) Is there a limit on mileage at which you do not want to buy one? ie at what point do they not make sense to get anymore
2) What are things to avoid? Known problems? Known pitfalls etc
3) What is typical upkeep on these things? Can an amature mechanic do alot of the work?
4) Where is a good place to look to buy these?
5) Are there any resouces I can reference on buying these? Advice etc.

Thanks again

Answer
Answer:
#1. 250,000 miles = after this point many need major transmission and/or engine work.
#2. NEVER buy without a Mercedes qualified technician PPI = Pre Purchase Inspection.
#3. First year average is $3,000.00 USD, personal DIY is very possible.
http://www.mercedesshop.com/shopforum/showthread.php?p=1100215
#4. Craigslist, ebay,
http://www.autotrader.com/
http://www.mercedesshop.com/shopforum/forumdisplay.php?f=24
and many other locations.

#5. Join http://www.mercedesshop.com/shopforum/index.php
post your desire to buy a MB in Diesel Discussion, many own gasoline and diesel MB, and they will be happy to offer advice.