I never buggered mine, and they were jaycar specials..I've seen mine not lock a few times because a door is not closed properly..

I guess it's possible, but it appears that if they won't go down, they normally pop open again. The alarm will arm, but your doors won't be locked.

Water is the biggest killer for the solenoids. Try and mount them so water won't easily run down the shaft, and run silastic around the casing where the fusion weld the plastic shell together. You know water gets them when they stop working and become very "ratchety". The little electric motor rusts and siezes. WD40 and a good wash down with metho normally fixes em up again..
Chris