Horn repair and worn commutator

[7_Zero]

I have a horn that works intermittently and was wondering what things to check to determine whether a horn needs a full rebuild vs just a cleaning and lubrication? Any indicators that might suggest the field coils needing to be rewound?

Sometimes when the horn works it will work for a few seconds and then just quit. It will randomly work again later, but sometimes it is minutes, other times it is days. I am wondering if the commutator is part of the problem as it is quite worn. Is this repairable? Can it be turned down, or at this stage would it be best to just try and clean it and run as is? Is it okay to clean the armature and field coils? Would this do any good?

The car has an alternator and was rewired a couple of years ago so the wiring is good. Not saying that the problem cannot exist in the wiring, but I am thinking the problem is in the horn itself.

Thanks!