[mikethedruid]

I believe this is an AC "synchronous" motor, no brushes. I don't think the speed it is turning is going to be affected much by a few volts low on the AC input. It is more likely to be a matter of dried grease in the bearings. See if you can disassemble to motor to be able to clean the bearings in some kerosene or mineral spirits, then lightly re-grease them with lithium grease, and re-assemble.