[Leo]

I had an early production set. In less than 1,000 miles the guides were worn so much you could wobble the valve and spring assembly by hand. At that time, (I know) they had teflon seals and (I'm not as sure but think that they had) guides made of a black material.

TFS rebuilt the heads, converted the bolt-down to stud mounts, put in bronze guides and black rubber seals.

They have never been installed since; they're actually for sale.

I too have heard that the teflon seals seal too good and would rather change valve seals than removing the heads for new valve guides.

Hope this helps!!!