Peter Frimberley wrote:

I think the overhaul was more about "behind the scenes" or
"undercarriage" stuff. These five units having been isolated on the
W&C had apparently become very different to the supposedly identical
1992 stock on the Central Line - e.g. I don't think the motor mods
that had to be done to the whole Central Line fleet when they started
dropping off had ever been done to the W&C stock

I don't think that last bit is correct..... the W&C was shut for a while
when the Central Line was shut. Since it was a safety mod you would expect
it to be done on all 92 stock at the same time (even though the ATO largely
caused the problem by putting more stress on the brackets than a human
driver would).