No, it can't penetrate anything once it's stuck. I know locksmiths say not to use WD-40 on locks, but it seems to do an excellent job on the Medeco plug locks to unstick them and keep them free.I use powdered graphite to keep locks lubricated. Works great. Not sure it will free up a stuck lock though.
JPRB
I agree, PB Blaster is probably the best penetrating oil out there.I use PB Blaster.
I buy it from Crest Ind. but I'm sure you can probably get it at Lowes or Home Depot.
It works when WD40 doesn't.