Any advice for knocking loose a stubborn pin?

Soak it in Kroil.

Have you got an air hammer with a small enough bit to punch the pins out? Or you could drill it out if you have or can make new pins.

All I can suggest is another lubricant. I love WD-40 but I’m also a big fan of Tri-Flow. It has little, tiny, tiny particles of Teflon that get in there and help you unstick things. You might want to give that a shot.

As a CNC machinist, I have plenty of fun tools at my disposal, some of which I have to use to extract/remove broken tools from parts. However, part of it depends on the type of pin, and more of it depends on how important the pins are.

Since we can generally make a replacement pin quickly and easily, we think nothing of taking a small drill and just removing the pin from the part by shredding it. That may be an option for you, if you can get/make a replacement pin.

Another possibility is temperature. Some of the things we put together are press fit in such a way that the only way to even get them to fit well enough to go together with a BFH is to put the internal part in the freezer for a while. (Not a normal one, but one that hits -80C/-112F.) While you don’t have that sort of freezer, the same result can be achieved by heating the external part (the part with the hole), assuming you can do so safely. That may give you just enough thermal expansion to loosen things up.

It would be easier if I saw the thing…

Needle nosed pliers?

WD-40 will only break down the rust on the surface. Try soaking it in a penetrating oil bath.

@jerv‘s suggestion about heating sounds like good advice.