You have probably found the cause but we had the same problem with our convertible. The first time I did dismantle the rear locker but after having the problem reoccur at least three times I found that with some juggling the locker can be left in place and just the rear side panel can be removed even leaving the seat belt in place.
Our problem was the left hand side and I found that after removing the complete drive assembly (leaving the glass in place) which is time consuming and fiddly the actual problem lies in the drive motor and gearbox. Due to the questionable design when in the car, the motor sits below the gearbox and what I found was that over a period of time the oil residue from the grease in the gearbox finds its way down the drive shaft and into the motor and contaminates the commutator and carbon brushes, effectively insulating the brushes from the commutator. Once the commutator and brushes were cleaned the motor worked as it should.
I don’t know if when designed there was an oil seal of some description fitted to the drive shaft but I couldn’t find any evidence one. After this happening to us at least three times I slipped an appropriately sized rubber grommet on to the drive shaft to act as a seal and it seems to be working so far.
Please note that when pulling it all apart make sure each part is marked so that it can be fitted back in the same position when reassembling, I found out the hard way when I had the motor case containing the permanent magnets 180 degrees out and when it was all back in the car and tested, one window went up as the other went down! If working with the top down, which is the only way I could see to do it make sure that when reassembling the glass is in the same position as the other window, reason the glass movement is controlled electronically by a timer and I would image that if the glass mechanism is not in the right position the motor would keep driving until the timer times out regardless of the position of the glass and you could end up with a bigger problem! As I said it is not all that hard just time consuming, fiddly, frustrating, that’s why there are no photos but we are working on Jaguars aren’t we.
Hope this helps.
Regards Brian, (Diane’s other half)