I've recently had the same/similar issue; the car going into park at slow speeds and MCU staying on after exiting the car.
Tesla said I needed a new seat base at a cost of circa £2500.
I took the seat out and found the location of the pressure sensor (circled red in pic). It's stuck to the base with adhesive.
I got the part number off the old sensor (1005424-00-A) and called Tesla to find they do in fact sell the sensor separately for £100.
I've now received and installed the new sensor. It comes preinstalled with an adhesive pad to attach to the seat base and there's just one plug to connect.
The car is now working perfectly.
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