Nearly all automatics have planetary gear sets. There are a few that are really manual trannies with a hydraulic or pneumatic shifter mechanism (the French made several), but all MBs are planetary -- three or four (possibly five) planetary sets per tranny.

A gear won't make any noise when not moving, and they only move when the car does, so a stationary "whine" is very likely the pump (the only part that moves with the car stationary) or torque converter, and torque converters rattle or clank, they don't usually whine.

The pump can be a bear to replace and set up correctly, so a rebuilt tranny isn't crazy at this point. $1600 is a good price, and yes, you DO have to be careful who you get one from, they aren't easy to rebuild correctly.

Check with the mechanic about a pump replacement, but I'd bet a tranny swap is cheaper.

Peter

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1972 220D ?? miles
1988 300E 200,012
1987 300D Turbo killed 9/25/07, 275,000 miles
1985 Volvo 740 GLE Turobodiesel 218,000
1972 280 SE 4.5 165, 000 - It runs!