Tamiya addressed the drive sprocket problem early in the run. The sprocket halves were a mm or so too shallow, to wit, the sprocket teeth bound on the inner part of the tooth hole in the track links. At first Tam produced a shim to go between the two halves, then changed the sprocket itself in subsequent production runs. My two Panthers are early ones, however I run aftermarket tracks and sprockets on them, but on one did switch back to the Tam sprocket, as the aftermarket ones were way off true, IOW they looked out of round, way out of round.
The barrel problem to the best of my knowledge is still extant. Everything works well, just there is some noticeable barrel side motion when he recoils. Daryl's little sleeve stops that. Asides from that, it's one of the best fighters OTB, and an excellent runner OTB with a straight forward relatively easy build.