What condition are the contacts in?
There is a considerable arc across the contacts each time the clock winds and this eventually burns the contacts and causes loss of material.
They can be cleaned up with some 600 or finer grit sandpaper and then by adding a diode across the coil, the arc can be dramatically reduced. The diode gives a path for the energy generated by the collapsing magnetic field in the coil.
There are special diodes for this application but the common 1N4007 will work fine. Anode of diode goes to negative side of coil and the cathode goes to the positive side (indicated by the band on the diode).