Is that push-pin release in the held-down position? If thats anything like the push-pins on PTO yokes I'm familiar with, they have to be pushed pretty much flush to release.
One sure way to make sure that the push-pin is not locking the yoke on the pto shaft would be to remove the push-pin entirely. On the other end of the push-pin is a retainer, usually a heavy circlip, sometimes a washer and cotter-pin. Remove that retainer, and you should be able to remove the push-pin by tapping on the other end with a pin-punch. Once the push-pin is all the way out, fish-out the spring as well. Then spray pblaster into that hole as well. When you get the yoke off, you can clean-up and de-rust and properly lube those pieces before re-assembly.
The stack of nuts inside the yoke to pry against on the end of the shaft is also something I've done to get a stubborn yoke off.
Take that zerk out of the u-joint cross to give a place to pry, if all this prying and whacking and such were to break that zerk off or tear-out the threads in the u-joint cross, that adds even more fun.
Theoretically, that u-joint cross should be assembled with the zerk away from the tractor pto shaft, so you could more easily sneak the grease coupler onto the zerk without uncoupling the driveline. Obviously, as long as that yoke has been on that shaft, that zerk has not been greased. Also, with the zerk facing the tractor pto shaft, when you push (sometimes kinda hard) the yoke onto the shaft if you over-shoot the lock point, the shaft could shoot through the yoke into the cross area and break the zerk. At this point, not worth pressing apart to do differently.
Wow... 48 posts so far... the Original Poster obviously not the first person to have cussed-out a stuck shaft.
