Use an analog multimeter to make sure you are getting the pulse to the coils on the relay as they should be.
The important thing here is figuring out if your relay is failing or is simply not getting correct instruction from the machine to do its task.
EDIT: This only applies if it's the two-coil kind. Is it one of those ones with only one coil that locks on via switches? Those are a bit more complicated. The switches on the relay only pertain to locking it on, shutting it off is moreso controlled by the score motor and other switches to disable power to the coil which also disables power to the "loop" circuit that is locking it on.