I'm relatively new at this, still I've had great luck with the G4 so far. I put in my new sensor on Sunday night. So far there have been a few periods of 20/25 point differences. As opposed to other sensors, which have been spot on starting on day 1 this one feels like it's always a little behind. It's not "failing" per say, but not up to the usual performance I've seen.
Maybe I'm just being too demanding, what would you do? Or more apt, when do you feel a sensor just isn't going to work?