I have a 31 year old home with a GFCI outlet in the garage that controls three bathroom outlets. Eight months ago it tripped and I replaced it with no problems until now. The GFCI outlet has tripped and I replaced it again and the same thing happened so it appears the previous outlet was okay so I reinstalled it. I understand moisture and dust can cause it to trip so I cleaned out each outlet - the GFCI outlet stayed on for a few minutes then tripped off again. The GFCI outlet is on the same breaker as exterior garage lights, and their electrical boxes are subject to moisture, so I'm wondering if any dust or moisture on the Line side can trip a GFCI outlet. Any advice will be appreciated.