The oil will penetrate that layer. Leaving that factory layer is actually a better idea to preventing the separation of the top sheet from the boosted sponge. You might have also noticed that in other boosting videos on youtube, some people lay a glue layer before boosting for the same reaon I have mentioned ealier - and that is to prevent separation.
Good question. Since most rubber glues are water based, how can oil get into the sponge after? Also, been watching a lot of these vid's, no one's saying how long baby oil effect will last but only it works. I'll study more before I move on. I have bought a few cheap unbranded Chinese rubbers off the net to study the quality between known brands. Curiosity might kill the cat but if I can turn stone into diamond, it'll be very rewarding, LOL.