A knowledgeable minority stresses that these flat-tappet engines run high valvetrain seat pressures and need high-zinc (ZDDP) oil, warning that thin modern synthetics can wipe cams and rockers. The commonly cited recommendation is a 20W-50 high-zinc oil except in very cold climates, and careful cold-start warm-up.
Oil weight and ZDDP requirement
Mercedes-Benz S-Class (W126) · ownership