I would disconnect the hot wire from the breaker (turn the breaker off first) and see if the problem persists. If so replace the breaker. If not you most likely have some water or a problem in a junction box somewhere.
GFCI units are susceptible to lightning and line transients. I have replaced the GFCI outlet in my post lamp 3 times.
Breakers do go bad, but it has been my experience that that is the LAST thing you should suspect. They are there to protect you.
Cliff(VA) Working EE