in Max's reply :
It works fine so long as no non-synthetic oil is used. It will condense and thicken-clogging the holes. Just like in the VC's I just re-conditioned for a friend.
I am the friend, but it wasn't me that ran with gunky oil. I got these covers from a forum member who had them given to him by a non-forum member.
( And Max is right - they were waaaaay gunky. Max didn't even see them in the original condition, I had already taken a swipe at cleaning them before handing them over to Max for blasting / painting. )
See below "Coming Attractions"