"When I stop the engine and then check after maybe 5 minutes, the fluid level is way above the max mark....

I am sooooo confused... "

Does this sentence mean that after 5 minutes or shut down, you start the
engine and then check the level? If yes, then you need to move the shift lever through the gears before checking the level. The tricky part is measuring the level just after filling with new fluid. The fluid is on the walls
of the tube. Takes a while before you can get an accurate fluid line on the
stick.

My experience on 3 different 300E's is simply to adjust the level with cold fluid to about 10mm below the minimum mark. I know from experience that
after running down the highway for an hour , the tranny fluid is heated up. Checking the level shows it to be between min and max. I've never had a transmission problem. Current '92 300E is at 219K miles with
transmission fluid and filter changes every 30K.

Common sense tells you there is some tolerance built into the fill level. Otherwise, there would not be a min and max mark on the dipstick.
I seriously doubt that shops are measuring temperature to get the fluid level
just right.

Steve White