Hello Richard,
The 1985 300D is a wonderful automobile. I paid a little bit MORE than the $4,100 almost 5 years ago. My car had 165,000 miles on it at the time. It had MANY maintinence records and was in VERY GOOD condition.
These days, that price MAY be a little high.............HOWEVER, no one will REALLY get a VERY GOOD car for less than $3,000 or so...........Remember that you should PLAN on spending a good chunk of cash during the first year to "bring the car up to speed".
CONDITION IS EVERYTHING! These engines can cost up to $6 or 7 THOUSAND dollars to replace and the transmissions are EXPENSIVE as well!
Find a good independant mechanic and let him (or her

) perform a THOROUGH pre purchase inspection for you. This should cost somewhere around $100 or so.
I strongly recommend a compression test as well.
No RUST.
Maintinence History
Remember......,CONDITION< CONDITION< CONDITION
The AC system can cost as much as $1,500 to get working properly!!!!
If the AC does NOT work, BULLSH*T!!!!!DEDUCT $1,000 from the price, and be FIRM!
There is more, however, do your homework and take your time.
This process will save your a*s in the long run.
Remember, ANY USED CAR is a GAMBLE......
Shop intelligently and you should do ok!
Documented REGULAR OIL CHANGES with a DIESEL SPECIFIC OIL!
Regular VALVE ADJUSTMENTS (recommended every 15,000 miles)
Enough already...
POST BACK WITH YOUR RESULTS
spo out 8)