That exhaust valve being recessed up into that oddball-shaped combustion chamber makes it difficult to get enough filler in there, for sure! I'm going to gaze into my crystal ball and make a guess that all your effort won't make a lot of difference, however. The angle of the exhaust valve stem is such that simply putting that little O ring at the top of the valve stem isn't going to make much difference in how much oil finds its way to the top of the exhaust valve guide. I have a sneaky feeling that either the exhaust guide has way too much clearance, or the source of the oil in the combustion chamber and exhaust ports is from somewhere other than the valve guides. I sincerely hope I'm wrong!
Edit:
One quick check for proper clearance would be to grab the tip of the valve stem with the spring removed, and shake it side to side. If there's a noticeable amount of movement at the tip of the valve, the clearance is probably too wide. You should be able to feel a little shake, but if you can see the tip of the stem move, you're going to have a hard time keeping the oil from running down the stem and into the engine.
Jerry
