I had a similar problem with my late parents everite mantle clock which they bought in 1952. About 10 years ago it started to play up and over a 2 year period I spent a small fortune on it and it spent more time being at the repairers than on my mantle piece.
In the end, I gave up flogging a dead horse, a local clock maker took out the movement and replaced it with a quartz motor. Externally it looks the same and it has quartz accuracy. The original movement is stored in a box but doing up mantle clock mechanisms is a fruitless task.
Just bite the bullet and do it.