Here's the method I use.

First, get the fluid to operating temperature by taking a 20 mile freeway drive. Then, park it on level ground, and remove the dipstick. Shift the car through each gear, and leave it in each gear for a second with your foot on the brake, when you get back to park, let it idle for about 3 minutes. Wipe the fluid off the dipstick with a lint free rag, and reinsert it. Pull it back out after 4 seconds and check the fluid level. If it is low, slowly bring it back to the right level, the distance between the MIN and MAX marks on the stick is 0.3 liters. I just had the same problem as you, turns out I was overfilled by a quart, took care of that with my Liquivac though.

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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.