If the car has 184k and isn't burning oil yet it might have one of the "good" factory engines. As I understand it most of them (mine included) didn't make it past 150k with a defective factory engine.

-Jason

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1991 350SDL. 230,000 miles (new motor @ 150,000). Blown head gasket

Tesla Model 3. 205,000 miles. Been to 48 states!
Past: A fleet of VW TDIs.... including a V10,a Dieselgate Passat, and 2 ECOdiesels.
2014 Cadillac ELR
2013 Fiat 500E.

It may already have a replacement block in the engine compartment as he states he has no records. Any mercedes dealer may be able to pull up the cars records to verify or not. THe replacements apparently are somewhat better. Whatever the real cause of the problem has never been totally rectified though.