1985 740 GLE B230F manual+overdrive 137,000
When the car is running warm (about 30-40 minutes of driving) the overdrive will not engage. I have taken off the od solenoid and blown compressed air thru it and changed the o-ring on it. I have drained the transmission fluid and refilled with ATF. Cleaned the solenoid contacts and checked electrical connections at both the shift lever and solenoid insertion. OD works great when car and fluid is cooler. I have read that it may be the acctuating pistons in the OD itself, 4th gear switch, or the OD may need to be rebuilt. Does anyone have any ideas. I love working on this car and it drives great.

Parts I've replaced in the last couple of months to keep it fresh...
Bosal cat-back exaust
alternator
flame trap
air-mass meter hose
spark plugs
tires
tranny fluid
trunk stuts
fresh paint
air filter
wiper arms
cd-player
tail light cicuits
fog light switch
throttle body clean is next...