My pins have run 3 years on a Kinze.  I had one go out the first year and it was covered under warranty -- no issues since.  I have been told that the Kinze pins are much less problematic than the Deere versions for what it's worth.  I always zero them to start the season, but have had to zero them in season a couple of times and that has always solved the wacky readings for me.  If a pin won't recalibrate, there is a good chance it is bad or you have something like a pinched wire.