Liquid wrench works very well for iron oxidation. It is probbably the least lethal of the chemicals sugested. Do keep in mind it is either(related to the anesthetic) and will make you nauseous in a confined area. Been there did that. Almost put me down for a while before I realised it. Effective stuff though, not too messy.
WD-40 is not volatile enough to penetrate. It is designed more for lubricating propperties and water displacement(WD). Gibbs and PB are somewhere in between WD and LW, but leave a goodly bit of residue. In fact Gibbs can double as rubber treatment, almost like armor all.
I prefer professional stregth ammonia for aluminum/iron corrosion. Most of the household grade brands are watered down too far to be effective. That works well for its application but has little or no effect on Iron oxide itself.