the more i think about this, the more i'd recommend getting a ESD strap from an electronics store and trying it out before any drastic changes to the guitar. the nicer ones have an elastic band the goes around your wrist and usually has several feet of electrical wire ending in an alligator clip that you attach to anything you think is grounded. i'd even try attaching it to the guitar bridge and seeing if it solves the problem. these ESD straps cost about $5 and they're useful to have around in any case, so little ventured, nothing lost.
martin's story of his atari illustrates the vulnerability of older equipment to this problem. i have horrible nylon ply carpet in my studio (previous owner o/t house) and if i walk in there with certain shoes, i zap my older gear. fortunately, i hate wearing shoes in the house so it doesn't happen too often but that's static electricity for you.
also, as andy said, we all love the yamaha guitars, not least the inexpensive ones. i have one of the pacifica's i picked up for $75 used, not cause i needed it but because it was such a cracking guitar that i couldn't stand to see it on the shop wall for that little money. so i gave the waif a home....
"Patsy had the drug tolerance of Keith Richards and the moral rectitude of Brian Jones." - Dr. Walter Bishop, "Fringe"