From whole fleet of MB that my family went via in last 3 decades, the most reliable was USA-assembled 1998 ML320.
13 years/130k miles in the family generated total about $300 parts who needed to be replaced (beside normal wearables).
Hard to beat this record, but than we bought that truck new and beside couple of oil changes I let dealer do during warranty period, no mechanic was allowed to open the hood.
Other sedans were bought used, so they always had need for TLC, but past models we drove never required more than $100 in annual new parts.
It took 2014 model where stupid Nox sensor cost over $500 not only becouse of high price, but becouse of SCN coding.