While we're talking about valve guide seals: I find it interesting that an old time machinist, who does lots of valve jobs on every kind of engine seems to think the seals aren't that necessary. He did a valve job on one of my bikes, no valve guide seals, it doesn't smoke and it doesn't use oil. I personally don't like chancing it so from now on I will bring him valve guide seals. He works mainly on car engines but has hundreds of tractor pull trophies, maybe 1000 trophies. It would be interesting to see what he could modify a TW head to do.