When I've "washed" ferrous bits and bobs, I will boil the parts in simple geen, the boil in water to wash out the detregent. The parts are hot enough to cook the water off them selves and boiling tempatures wont effect tempered steel. Wd40 sprayed on to hot metal seems to flow and suck into crevices. I've never tried this with a complex mechanism, but as far as solvent soaking I like kerosene. AFAIK WD40 is kero with a detergent and a manly scent added.