Tub back removal
The best way to do it is to balance the tub back on 2 chairs so the cylinder hangs freely with towel or blanket underneath the cylinder so when it breaks loose it will fall on the blanket.Heating it may help.But you are only able to heat the outer bearing not the inner bearing.And the inner bearing is the one that was exposed to water.If you have a pointed chisel you can try centering that on the shaft and give it a good blow.Be careful not to damage the shaft end.Sometimes short hard blows work.It will break loose.Wish I was there to do it for you.Done it many times before.Just keep trying.And walk away from it for a while then go back and try again.And as far as the spot welding I would say no.Let us know when you get it apart.