RE: Removing engine room fuel stains
Clean it up as well as you can first. Napatha is a good solvent for oil/fuel stains to get everything possible off by solvent interaction. Then there are a few different things you can try. The first I would suggest is FSR, a blue gel from Davis that contains oxalic acid. It will bleach out stains and has worked very well for me in the past. Barkeeper's Friend is a scrubbing powder that has oxalic acid in it as well. You can scrub with it, and make a paste and leave it on the site.