I pressure washed it a 2nd time in the cracks as good as I could, still nothing. So I broke down and removed my other 4C from its mount (that was an ordeal in itself) and mounted the stuck one in its place.
Sprayed penetrating oil in all the cracks and on the screw and everywhere I could that would have things moving. Figured what the heck and tried to turn it by hand since now I could get all my weight on it. Sure enough it was really tough to turn but it was moving! I was a little hesitant because if I closed it all the way, what if I couldn't get it back open!?! I kept going though, each turn was progress after all. I could see the now exposed slide and it was just covered in dirt, caked on hard. After closing the slide all the way I tried a putty knife to scrape it off, then I thought, "Why am I dicking around like this?" and got the angle-grinder with a wire wheel. Even that took some effort but it slowly all came off. As I said before, I think someone dropped some dry quickrete on it and never cleaned it off. It was a major pain!!!
Okay, cleaned off the slide, went to try and open it. Slowly but surely it was opening, a lot less effort this time but still a fair amount of resistance. Then with about 2" of the slide sticking out the back it didn't want to open anymore! ACK!!! Closed it a bit to look at the slide and such, noticed some welding spatter globbed on in a few spots. Changed out the wire wheel for a flap-disk and ground them smooth. Slide opened up all the way nice and easy and pulled it out! WOOHOO!!!
It was DIRTY inside, it's literally like someone filled it with mud, then put the slide in. It is all full on the sides, and I can squish it with my finger, it's not rust it's dirt!
Now I just have to work on getting the base off, but that is another project for another day. It's going to need some acetylene on that center bolt & the lock-down to get it free. For now I'm going to pressure-wash the parts and stick the base/static half back in the e-tank so it can work on the bottom.
Still could not get the set-screw out that hold the front collar. I literally chipped the end off a screwdriver. I'll try some heat on it too but I'm afraid that is going to have to be drilled out. I even tried my impact driver with no luck.