I have an E-Flite MCX which has recently started to drift in little (2') circles when I try to hover. The nose is always facing the same direction, but high, low, wherever I go it looks like it is revolving around an unseen point. Since I'm just beginning with helicopters, I have broken and replaced upper blades, lower blades, the fly bar, head and even the landing gear(!) but the flight problem seems to have crept in somewhere along the way and I don't know where to begin.

Another thing I noticed with my MCX that has started to happen recently is that as the battery gets low (last 20 or 30 seconds of flight), the heli starts to pirouette loosely to the left, tail following the nose in a spiral. I just land and turn everything off, but I'm wondering if one of the motors might be wearing out. If so, I guess I should replace them both, right?

Any ideas about what I can do to correct these issues?