Had 3rd gear on my power quad go out on a 7400 at about the same hours.  Fixed it myself for arounnd $2500.  Ended up also having a groove wore in a gear where the friction discs drive from (on the inside) that looked so neat I originally thought it was machined that way and was supposed to have a snap ring.  I had never had a transmission out of one before but it wasn't too bad to do.