Hi Brad,
Sure that's fourth gear and not third? Third gear is rather notorious for breaking. I haven't heard of problems with fourth but it doesn't mean it won't happen.
Anyway.... I think you'd be risking big serious major doo-doo if you run that bike with a missing dog. It only has three to begin with. You knock one off and now the remaining two have to bear the drive force that three used to bear. This will likely lead to quicker failure of one of the two remaining. Now you're down to one and guess how long that puppy is going to last. Also a broken dog floating around your tranny can easily get caught in some other gears as you're going full tilt down a straight away and lock the whole scoot up. Guess where you wind up???
The MT gearbox works fine. Wider ratios but just fine. I ran the wider ratios in my bike for desert racing back in the 70's. I don't remember specifically but I think fourth is the same between the CR and MT. If so just take the good fourth from the MT and pop it in the CR. (Maybe someone else can verify this.)
HTH,
Loren