gen 2 XMRs have helical cut splines, which are stronger going forward than straight cut splines....the xmr is he only one with helical cut splines, from what I understand....that is one reason why everyone upgrades to the xmr diff. Another reason is the casing is bigger and stronger than the standard diff....which means it can take more abuse....as far as mud n wheels goes, I'm seen his videos. Would be interested to see what he does to improve them and see pics of his work. If I ever break one, I might consider one of his depending on his price and quality of work