I don't think that actually works because with the engine off, you are still loosing oil.
Am I wrong? 
yes you're wrong, though it makes no sense to me either... the prop / crank / pistons, camshafts, etc. etc. etc (and I presume oil pump?). are still moving due to windmilling prop, yet in the game, your oil pressure will remain, if you have the engine "off".
and as to the others, I just noticed today an oil hit to my own plane gives a brief FR hit all the way to 4-5fps (normally 60fps pegged), maybe 1-2 seconds, then it recovers and framerate back to normal.. never used to happen to me before!
getting oil hit on someone else doesnt do it at all.. even weirder...
what it kinda seemed like to me is it was loading texture for oil covered windscreen, and black smoke I could see out of the cowling out of front view off to the side.... maybe cuz I am running wider FOV than previously, its drawing close smoke and that takes more computer power? I dunno..
