I had the benefit of owning for 3 months an '87 300D with a transmission fluid temperature gauge. It takes about 20 miles of driving to get the transmission fluid to a steady operating temperature of about 180*F. It's at that temperature that the dipstick reading is accurate. There's a guidance spec of 8-10mm below the min level for cold fluid. You'll overfill it if you set cold fluid within the MIN and MAX lines.

Sixto
87 300D