About a month ago i noticed a little oil seepage from the bottom of the case.. I bought a gasket kit, piston kit and took it to my local shop.. they put it all together, we rode for about one hr and i noticed a vibration so i took it back in.. he said the flywheel nut had come loose and fixed it.. we went out the next weekend and as soon as my son got on his bike he noticed it was stuck in second gear.. i was able to shift it with my hand but only with a little force.. any ideas about what or why it would do this?? has something suddenly woreout?? thanks in advance!!