You should be in the same boat as John for at least a while unless your birfs are already well worn. I found a sweet deal not long ago that I didn't think would work for spares for me, so I passed it off to John. Lets just say he will not be breaking birfs anymore. Birfs do exponentially better on crawler rigs with little motors of course, so just be mindful to turn as little as possible any time to have to "get on it" and I bet they'll last a while. You got a couple spares for GSMTR? We've got a few experts at field replacing.