Penetrating oil has to be of low viscosity and therefore is generally volatile and will evaporate - at best - in a timescale similar to water. WD-40 takes longer, but I have known one case where a primer I'd 'deactivated' with it came to life again later - though I can't remember the exact circumstances.

Slightly heavier oils like light machine oil (eg 3-in-1) have generally worked well on the few occasions I've needed to do this. I certainly haven't tried the hammer test afterwards though!

I think that machine oil is used in inert collectors' cartridges, with the addition of some oily sand or tissue inside the case to maintain the vapour-pressure of the oil in the primer, to stop it evaporating over longer timescales.

Presumably the oil works by reducing the friction between priming compound particles so that less heat is generated by a 'normal' impact, and acting as a heatsink to absorb such as there is. I doubt that it kills the reaction chemically.

Regards,
MikB