Heat treating is not necesarily the answer. Although heat treating does make the metal stronger it also makes it more brittle (ie lowers its fatigue life). My motor mounts failed on my warrior too and it was definitely a fatigue failure. I know because I see them everyday with my job. Fatigue failures are usually the result of something else being loose, like other engine bolts or its a natural frequency issue.
I am almost 100% certain that yamaha would have found a natural frequency issue with these mounts if there was one. I can also tell you from experience that these mounts are so ridgidley held that there should be no natural frequency issue either.
In my case there was another engine mounting bolt missing which I am positive caused the failure. I bought new engine mounts and replaced the bolt that was missing. I suggest you check all of the other bolts. Make sure they are there and then make sure they are torqued down correctly. Torque is critical here. Don't just bear down on it with a ratchet. I used to think people were crazy when they told me that torquing was important. My current job has taught me that I was dead wrong.
