1. Bad surface finish on valves.
2. Guide material was junk.
3. Possibility of an over-efficient valve seal in an
oil restricted environment.
Pick one or two. Haven't finished up the analysis. Leaning towards valves stem surface finish on some custom hollow-stem Ferrea valves. Talking with other builders, at least one had seen this before and labeled it a valve stem problem.
However, it wasn't a geometry issue. Guides were worn concentrically on all valves instead of in one axis and with a T&D race roller rocker arm leaving a .050-.055" pattern on a valve stem, there is little possibility of a side load.
My reluctance to give a clear answer was because I can rule out geometry but I don't have a 100% target to point my finger at right now.