French clock

[Terry]

The clock itself ticks for about 15 seconds if you nudge the pendulum, then stops. 

It sounds as if it might only need cleaning to restore it to full working order - which would increase its value (whatever it is!). On the other hand, a pendulum clock my late father in law owned had a very cheap movement fitted and the problem with that was that an un-bushed bearing on a pinion at the start of the gear train had gradually worn a slot in the frame (because of the continual pressure from the spring) until the teeth were just barely making physical contact and the shaft was no longer perpendicular to the frame! If the cabinet had been in better condition I would have considered drilling out the frame and fitting a bush to rectify the problem.

If you want to attempt it clean it yourself, make sure that there is a good strong strap round the main spring to stop it unwinding involuntarily!