123 300D driver,

Do a search. This has been covered fairly well, including some pretty good hints at how to best get to certain fasteners. Driver's side is harder to get to than passenger (US driving configuration). On a 300D with a turbo the passenger side may be more difficult.

Have someone try starting the car while you watch what the engine is doing. The driver's side is the one that can go into tension, which, when it fails allows the engine to rock back and forth pretty hard. Banging on the passenger side may be intake and exhaust system related. Good luck, Jim

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Own:
1986 Euro 190E 2.3-16 (291,000 miles),
1998 E300D TurboDiesel, 231,000 miles -purchased with 45,000,
1988 300E 5-speed 252,000 miles,
1983 240D 4-speed, purchased w/136,000, now with 222,000 miles.
2009 ML320CDI Bluetec, 89,000 miles

Owned:
1971 220D (250,000 miles plus, sold to father-in-law),
1975 240D (245,000 miles - died of body rot),
1991 350SD (176,560 miles, weakest Benz I have owned),
1999 C230 Sport (45,400 miles),
1982 240D (321,000 miles, put to sleep)