I got a tingle from a wet saw (tile project) the other day, and was curious as to why the GFI didn't trip. I punched the test button and sure enough nothing happened. So my question is, do I just replace the recpticle with a new one and be done with it, or do I worry about what caused it to go bad in the first place? It is an outdoor recepticle on a detached garage with a leaky roof, so I worry about it getting wet. But there is no obvious signs of water in the electrical box, and presumably the outlets say "test monthly" (I wonder how many people do, but I'll being doing it more often from now on) for a reason. The outlet is about 8 years old. So how common is this?