good penetrating oil?

Castle THRUST is the absolute best I've ever found. I use it daily since I do this for a living. PB Blaster can't hold a candle to it. It's a little hard to find in some areas but well worth the search. It has ionizing formula that reacts with the rusted parts to unlock them. I buy it by the case so I have it when I need it. Works great!
Another good one is GM Heat Valve Penetrant. that works pretty good & is available at most GM dealers.