Transmission Conundrum



I have a 1997 BMW 528i with 70K miles. After a snow storm in December while driving on wet pavement in Drive gear, the car flipped back and forth between D and S2 on it’s own. On one occasion after restarting the engine the emergency transmission light came on and I could smell fluid while driving. My mechanic did a transmission flush and replaced the gear sensor trying to avoid replacing the transmission. After the sensor replacement the car was fine until the recent blizzard in DC. After sitting on the street for a week the first time out again on relatively wet/dry payment it started flipping gears again and the emergency transmission light came after restarting the car at a gas station again with the fluid fumes.

Question: Could something be burning the sensor out or do I need a new transmission?