For the 722.1 transmission with a 5 cyl. engine, it takes about 4.8 liters (or 4 quarts) to refill. When you refill, put only 3½ quarts in at first. Then, start it, and go for a 20 mile highway drive to get the transmission fully warm. Then, check the fluid on level ground with the car in park, still running with the parking brake on, and add small amounts until it's at the MAX mark if needed. Be sure to wipe the dipstick off with something that won't leave lint (wiping it off with your fingers and wiping them on a cloth is good).

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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.