Update: it's at my repairer/modifier of choice and the way I understand it so far, they got inconclusive results on measuring the whole caboodle but it's very probable the servo on the Escap is borked.
The route forward will probably be some sort of optical sensor drive system, either using the existing motor disregarding its servo, or one of a batch of Maxons they happen to have lying around, although these are ball bearing variants and as of yet they're not sure of the suitability of those for use in a TT.
On the upside the arm will be wearing an SPU Royal N when the PT returns.
I'm sure these particular folks (designers of Pink Faun gear) will come up with something rather more advanced, not to mention stable, than the 1983 Arthur K. servo board, too.
I'll keep y'all posted.