As a diesel nut with some long experience running diesels I find it odd that MB or most diesel techs do not recommend overhauling the injectors on a somewhat regular basis (100K). I have found on most engines a marked difference in performace after the injectors have overhauled. This is a cheap easy fix. Better economy, less smoke, easier starts, quieter running etc. etc...
I realize it will not fix a real problem but many problems may not be real if this fix (service) is not overlooked.
Anyway just a comment.

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Mark
82 300SD 110k
91 Caprice SS
92 Jetta TD
97 Cadillac Concours(300hp)
84 Celebrity 4.3L diesel