I would say start with the fuel filter, maybe it clogged up. Also, this is an M110 car but is fuel injected right? I believe it is a mechanical fuel pump. Make sure it is pumping fuel to the injectors. Try starter fluid at the intake plenum to see if it will start using that stuff.

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2006 BMW M5 "Heidi" @ 109,000 miles
2005 MBZ C55 AMG "Lorelai" @ 165,000 miles
1991 MBZ 300E "Benzachino II" @ 165,000 miles
1990 MBZ 500SL "Shoshanna" @ 118,000 miles

(On the hunt for a good used M103 engine as of 6/10/23, PM me if you have one to sell!)