I was recently given a 2000 Ti Fat bike from a friend. After riding it for the first time, I noticed the chain slipping and decided to take it in to my local shop for a basic tune up. Just got a call that the middle ring had 3 teeth missing and needs replacing. The whole bike has shimano XT and XTR components on it. The replacement part is going to be a Deore. My question is, Should I just replace the entire drive train with something more modern? Sounds like parts are hard to come by for the current set up.