Aside from the diesel engine itself, there are some pretty comprehensive maintenance suggestions for the W126 chassis cars cars in the buyers guide found in the website
www.mbcoupes.com
While I co wrote that back in 1998, it was pretty well researched, and widely acclaimed as good, over the last 10 years.
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1991 560 SEC AMG, 199k <---- 300 hp 10:1 ECE euro HV ...
1995 E 420, 170k "The Red Plum" (sold)
2015 BMW 535i xdrive awd
Stage 1 DINAN, 6k, <----364 hp
1967 Mercury Cougar, 49k
2013 Jaguar XF, 20k <----340 hp Supercharged, All Wheel Drive

(sold)