Oil pooling on exhaust valve.
Doogievig,
I guess that it did not smoke or otherwise act funny on the stand? Were you there? I can't visualize oil puddle on the valve. It's inverted right? I guess that this was the only time you saw it, did you rotate or crank the engine to create any oil pressure? Is it weeping out? Did you pull a valve cover and take a peek?
Best of Luck!!!
Marion