isn't this oil a result of the vacuum that's in the intake tract after the throttle body slams closed? like after a high speed blast, and then getting off the throttle and coasting down? the pistons are still trying to pull a lot of vacuum, so it's drawing oil back down the exhaust valve guides because it has to pull it from somewhere when the throttle body is closed until the rpm's subside and pull less vacuum?
i'm certainly no expert, but it seems it's something i picked up from more of the knowledgeable members around here. imho opinion the catch can won't catch this oil as it's not coming from the valve covers to the intake and then to the delete plates (it looks like it's on the bottom of the butterflies and not the tops), it's drawing down the valve guides and seals, if i'm imagining this right
also you didn't say if you're fi...isn't that where the catch cans help the most...the extra boost escaping back thru the pcv system and capturing it before it's reintroduced into the intake tract...
i probably have it all wrong