Oil leak is fixed. I took the top off the mower, reseated the correct O ring, got some locking washers, the kind that grip, and re-bolted the top back on. No more flop or wobble, and the oil filler is now squished down firmly so no more oil leaks.
Now its just the engine issue. It really feels like the problem is TOTALLY different now than when I started this thread. The sounds are nothing like the movies any more. Now my inexperienced ear says it kinda just sounds like it is misfiring. Would that make sense? It does it less and less, the longer it runs. After 10-15 minutes, it barely does it at all. I don't know anything about it, so I suppose it could still be fuel delivery. But if it were a fuel flow problem, wouldn't it have been less of a problem when the mower was running at lower RPMs, and more of a problem at the new higher RPMs? Plus if it were a fuel delivery problem, what would cause the problem to go away once the engine heats up? What creates the spark that goes to the spark plug? Is it possible whatever that is, is bad on this mower?