My Load-rite rollers swivel all over the place.
Boy I miss that old Blazer!!:'(
My last trailer was also to move, but were froze like yours, but they were froze in perfect position, and I left it alone!
A friend of mine fixed his, and the only way is that you will have to get the boat off the trailer and get all the bolts out, clean and replace with SS and all will be good again.
Now there is a small problem here, SS is not as strong as steel, you should use grade 8 bolts here cause they take a lot of weight!
But if you use steel they will rust again and you will start to stiffen up.
My buddy used SS and in 4 years 2 bolts broke!! I would use Steel and keep well lubed!!
I don't like grease or never seize here because it attracts dirt and holds it, there for it will start binding.
Just rinse with freash water well and when you can just spray the crap out of them with a good oil!