Hm, they could just clean off the majority of the excess oil with some substance that is oil dissolvent... though it does make for one long pain in the ass procedure if both the sonic and oilshower precedes it. It's either not a daily procedure, or 'formers did think up something convenient method to quickly disperse oil.
I could think up all kind of weird shit now that I'm doped up on ST, like some light-based disperser if they're in a hurry and can't wait, just stand between two panels, flash, you're good to go. I'm not sure if it could work because of my limited knowledge in synthetic oils, but hey, did they ever even explain sonic showers? If they did, I missed it. God bless science.