[BRG75]

I have found this from a rover 75 forum (not this one) back in 2011.

The writer had the same problem, courtesy of a gate post, and was ascertaining what options he had.

In short, the motor in a power-fold mirror, is the same in both the O/S and N/S mirrors.
Of more significance, he states that a non power mirror can be built up as a power-fold mirror in 30 minutes, simply by adding the motor. Obviously provided that the wiring and switch are already in place.
He is talking about the bullet mirrors, which I think are the early ones, but this may well be the case for the later ones.

Having stripped the mirrors down i can confirm that the motors are NOT handed so left fits right and right fits left. Also the ONLY difference in the powerfold bullet mirror and a standard bullet mirror is the motor itself. In short if you buy two N/S powerfold mirrors from Bob you can turn your standard mirrors into power folds in around 30 mins