It's a better release agent but I've used wd40 a lot as well, and though it's not "as good" it works infinitely better than nothing at all.Never used PG, maybe I should. Always used WD, found it good for cleaning crud off my guns before I oil them. Think with WD you need to start using it a few days before you want to do the work.
Engine oil? hydraulic oil , what I found is hydraulic oil from old tractors is excellent as a rustproofer/finish on old tools etc, seems it soaks up water from condensation in the tractor and goes milky brown, that applied to a spade/tool or similar seems to soak in and give a rust proof finish, works loverly on old tools that have had a light wire brush to remove loose rust first. old gearbox oil ,used , also if mixed with parafin, same as used engine oil mixed with parafin works, but hydraulic is my prefered choice, as long as you are not painting it. Artherwhats the engine ,arthur?