It may just need cleaning. Cased clocks gather dust and airborne particles quickly.
You could try one of the "dry" duster cans used for computer keyboards (I have "Endust") just keep upright (the can, not you!) and do NOT shake - it emits a hi-pressure neutral gas that will clear accumulated crud.
If that doesn't help get a clockmaker to give you a quote.
howtomendit.com for free repair help, information and advice.
Try fixfault.com to fix wrist watches.