No promises it'll fix the issue at hand, but it's certainly a contender. When they fail they can cause strange issues or no symptoms at all for some people. The most common complaint is warm starting issues where the car's sat for 15-30 mins and either refuses to start, cranks for longer than normal, or "chugs" for a few seconds when restarted. When working properly, the M117 should be "diesel" fast starting, basically a flick of the key hot or cold and it should just about jump to life.

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Current stable:
1995 E320 157K (Nancy)
1983 500SL 125K (SLoL)

Gone but not forgotten:
1986 300SDL (RIP)
1991 350SD
1991 560SEL
1990 560SEL
1986 500SEL Euro (Rusted to nothing at 47K!)

Gone and wanting to forget:
1985 524TD 167K (TotalDumpster™) [Definitely NOT a Benz]