There has been quite a bit of chatter about HPMX carbs on thesamba lately. The early versions seem to have quite a few issues, but since Art was able to set them straight on a few major items, seems like most can just slap them on and go. I think the version 2 came out last year?
Something like that.
I've also heard you want buy your HPMX carbs, then send them to Art so he can re-do them. This is for new carbs. BUT, I've heard tons of guys having good luck with them lately. The quality must be getting better.
Shafts wear and yes you can get them rebuilt, but any used carb will likely have vac leaks up the ying-yang. My 2 cents would be on HPMX units unless I could score a good set of low mileage webers.