Transmission

Ok so I have a 2011 680 Rincon. 3 years ago it wouldnt go into reverse, I took it to the dealer and they replaced the 3 part gears and it worked fine. They said they were worn out and I still have them and there is absolutely nothing wrong with the old ones. Soo anyway 3 years later it wont go into reverse again and to top it off the transmission completely locks while rolling backwards in natural and drive running or not.. It's pretty scary because it locks up solid and wants to flip over.. not cool.