PB Blaster and Kroil are both excellent. I have gone back and forth in my opinion of which is better for automotive wrenching. A few years back Popular Mechanics did a little test and good old (and often forgotten) Liquid Wrench came out on, or close to, the top.
In a pinch ATF (Automatic Transmission Fluid) and acetone mixed 50/50 also is a good penetrating lube, but it is of course highly flammable.
For the OP, glad to hear you got the stem removed!