i always refer to issues like yours as "bleeders:.i've built them before and never found a comfort with them. there could be a multitude of small things that can contribute to this but in my experience the majority "bleeding" is in the bearings (rods and mains). there could be a cam bearing issue and i'm sure edm tappets don't help matters but i doubt the main cause. my opinion is if your going as far as pan removal then go the extra step and get the engine out on a stand. it's the only sane way to diagnose the issue and solve it.