Chiphead,

Personally I do not like the O-ring seals, they really let us down sooner or later, and as the guides looses, they can do nothing to stop the oil coming down. If You can use the umbrella, go for it. You can even leave the O-ring and the umbrella. Or You can use the teflon. But the fact that it will induce valve guide wear is really a fact, and when the guides get really loose, it will not stop the coming down oil. And it may happen before You think it should happen.
Now if I were You, and considering the engine type, i'd go for the umbrellas. Just the 0.02.


Alexandre Garcia