For 2 years I have run B100 in the summer, blending as needed in the winter. Biodiesel will deteriorate rubber fuel system parts faster than pump diesel. Last fall after a period of "spirited" driving in the '99 E300, I noticed a faint fuel odor when parked, a small puddle underneath, opened the hood to find the IP leaking. Ray @ RDM in Tiverton, RI replaced the o-rings on delivery valves, shut off valve and plastic lines. IIRC the SOV leak was hard to spot & $$ to replace but the car runs great now. I'd have to go over the PO's service records, but I think all that stuff was original- not a bad run.

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1991 300D