Jason,
If you can find a W210 / 606 of the years 96 to 99 with 150K or less....JUMP ON IT! Thats a find! There were only a little over 7,500 brought into the US...total! I would'nt even equate their durability until they have at least 150,000 or more on them...they should last 2 to 3 times that.

The 98 E-300TD I have now is the best performing and economical MB out of the 3 I've had. Believe me, i loved the two W-126 MBs when I had them but....
The 606 engine whether its Turbo or non-Turbo is a great performer and generally problem free. The most noted and common problem you will find in talking to an owner or in a search on this site is the "leaking clear plastic fuel lines" which seems to plague them after they age for 8 to ten years. Change them...thats an easy fix which has nothing to do with the inherent durability of the 606 engine.

__________________
FRED

Daily Driver: 98 E300TD 199K
Hobby Car: 69 Austin Mini
Past Diesels: 84 300SD, 312K
87 300SDL, 251K
94 Chev. K-1500 6.5Ltr.TD, 373K