I own an aircraft that has experienced a VOR/LOC failure consistently in flight but when on the ground, it works fine. It is being sourced by a Garmin 430. It fails in GPS mode, VLOC mode. Doesnt matter. Any mode, any station tuned, any flight plan, no flight plan. Always broken. Get it on the ground, the avionics guy tests it, it passes every test. Been to two avionics guys now. Suspect a bad NAV board. Probably going to replace it but figured i'd just see how many other people have seen a problem like this.
A broken VOR - YouTube