I put a couple of pics up in the photo galleries of the internal of the auto TX.

An internal spring broke which is part of the switching mechanism and supposed to flick the contacts from one tap to another in a snap type action.
The contacts didn't close properly and it started arcing, hence fluctuating voltages.

I think it is repairable. Up to the asset owner to decide if the TX is toast or reco.

The product of rotation, excitation and flux produces electricty.