WD-40 does do a pretty good job of gumming up a trigger but it's definitely not the worst thing a gunsmith will run into. I once had semi-auto 22 come into the shop because it was frozen solid. I soaked it in Varsol overnight with little effect. I finally warmed up with heat gun and gut the breech bolt to move; reluctantly. Turned out the owner had oiled it up to put it away and had used olive oil! This was way beyond gummed up. Didn't rust though. GD
