I don't think you've got the same problem as I'm having. Mine is just purely a matter of how long the car sits. If it sits for a few days it starts very rough and somewhat noisy. Warmed up and sitting for a few hours I would never have the problem. I'm beginning to think I might have injectors leaking down - even though they were recently cleaned.

Your problem is so intermitent that I think I would try another oil check valve. There's a new style part and apparently even the new style sometimes doesn't seat just right. I've thought about doing this myself - only because it's fairly inexpensive.