Cindy and John, and Other folks.
I recommend you place some grease, yes grease on the
end of the buld that goes into the bulb socket. This will prevent the bulb contacts from becoming corroded.
I use 'White Grease' it is also callled 'Brake Grease'. Dip the end of the bulb into the grease, wipe off the excess, but leave all of the bulb contacts coated.
Should be used on any bulbs exposed to moisture.
Pleased you found your problem.
DR. John