I have the centre push and mine has recently failed for a different reason.
The spring loaded contact on the wheel boss was touching just the outer few mm of the copper ring, with a bit of an overhang. The tip of the contact had worn leaving a lip on one side and eventually this lip tag touched the plastic surrounding the copper ring causing the horn to become intermittent/non existant.
Removed the sprung contact and introduced the tip to Mr File and it's all working fine again.