On the subject of penetants, I've used Kroil when I worked at a
factory, seemed like good stuff but haven't seen it anywhere else since
I left there.
I've been using that "Deep Creep" made by Sea Foam; don't know how it
ranks as a penetrant (seems to do the job) and it's fairly expensive,
but what I REALLY find useful about it is that it will spray upside
down(!), which in my opinion is very handy & practical.