1981 300SD Valvoline 10w-40 all year, change every 5 months which is about 5K mi, odometer is non functional.
1982 300D Mobil 1 synthetic 15W-50 all year, change every 5 months or 5K mi, slow odometer is reason why.
Mann filters only on both cars.

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'81 MB 300SD, '82 MB 300D Turbo (sold/RIP), '04 Lincoln Town Car Ultimate

Sooner or later every car falls apart, ours does it later!
-German Narrator in a MB Promotion Film about the then brand new W123.