[McMurdo]

Maybe just needs a clean and lube? If it used to go backwards sometimes, that sounds like the one-way ratchet was sticking or worn, synchronous clock motor designs can often start up forwards or backwards as they choose and are prevented from continuing backwards by a ratchet.
If you get a reading through the winding then I suspect its little holiday has allowed it to go a bit stiff.

Sounds an interesting piece, do you have any pictures? Google shows there was a westclox mantle clock on ebay which the seller described as being marked 'EM21'. Our local newsagent used to have an electric clock in the 70's built into an art deco illuminated Benson & Hedges sign.