It sounds like the slugs have worn out. It's highly unlikely that the track would have opend up. You can purchase replacement slugs through Hobie, however they don't make the balls anymore.
After having one of the balls pop out of the track right after the start of one of the races at the 2012 NAC, I would never use the balls again (granted, that was the one and only time it's ever happend to me). I think the traveller works just as well if not better with two slugs anyway. If you're having trouble with it sliding, try shooting the track with silicone. You can also run along the track groove with some wet/dry sandpaper sprayed with WD-40 to smooth out any burrs in the track.