Having no electrical power available at the storage facility, I had to unscrew the broken leaf's set of 4 nuts on the U bolts with just a ratchet. Had to use an extension bar to undo the rusty nuts. Used PB and penetrating oil. Took a long time and awkward.
Then I drove the trailer home. With power available, I cut the U bolts across the top with a dremel drill. Quite a snap open at the last 1/16th of an inch with the first U bolt. So much so I tied the 2nd U bolt up with rope. Did the job in about 15 mins. Much easier !
Getting the rusty bolt out of the fixed shackle was tough. I finally cut a short piece of 2" X 4", drilled a 1" hole in the middle, about halfway through, placed this over the bolt head, and then put a strong short clamp over the wood and and the other end over the end of the bolt behind the shackle. Turned the clamp handle with an extension bar, and finally was rewarded with a short snap noise, indicating the bolt had shifted. The trouble with my bolts were that they had splines at the head end, so could not be turned.
This was only partially successful, so I eventually used a large sized thick wrench over the head, with a short thick piece of metal over that. Then the clamp. (a large sized socket, into which the bolt head would fit, would do as well). Obviously, the other end of the clamp was over the other (the screw end) end of the bolt.
At any rate, mission finally successful. Both new leafs now installed and torqued according to Dexter specifications (despite the falling snow !).
Thanks for info on the wet bolts.