The MB maint manual has a procedure for checking the transmission fluid level. One for a cold system; one for a fully-warmed up system. Automatic transmission don't warm up 'til you've driven 15-20 miles.

Cold approach - with engine cold and on level surface, start it up and shift through all of the gears a few times. Place in Park, then remove/clean stick. Reinsert and remove. Level should be no less than 10mm below the low mark.

Warmed-up approach - drive car for 15-20 miles(20 might be better in winter). Same as above-level surface. With engine idling, remove and clean stick, reinsert, remove and check level. Should be no higher than MAX mark on stick.

Some believe that the warmed-up approach is the most accurate. In my experience, if it passes the cold test, it will also pass the warmed-up test.

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Mike Murrell
1991 300-SEL - Model 126
M103 - SOHC
"Fräulein"