Hi guys I have a Ktm sx-f 450 09 model and it´s gradually become harder to start to the point it won´t start and now shoots blue flame aswell as popping back thru carby Mechinacs have told me that carby is fine values clearances fine that something Mechinical in top end has gone wrong that they need to pull it down further to inspect,,after looking at it further I´ve been told it was piston and ring problem, and they quoted $2200 to repair!! Does this sound like a legit diagnostic