Bike idling nicely in driveway,new riding gear on,jump on my '07 wr450 pull in the clutch & when I put bike into 1st it jumps ahead & stalls as if the clutch was out. Lever adjustments did nothing. After several tries & the same result put it back in the shop. &%$#@!? Call my mechanic buddy & he says clutch plates are hanging up & not disengaging after bike sat all winter & I should drain the oil,pull the clutch cover & check to see whats stuck.Go to reinstall the drain bolt after draining the oil & it won't tighten. The threads in the case are stripped!! Looking for some advice on how to fix both issues. NOT a good way to start the year. Any help much appreciated.