I agree with rScotty. I think you have two separate issues going on and are unrelated to one another. One question in my mind is you said you have used the top of the loader for a seat when it was on the ground. When you sat on it, was the cutting edge of the bucket flat on the ground or raised a bit as it is in this video and just sitting on the back bottom edge of the bucket, thus creating a lever? Have you ever had the bucket sitting exactly this way before the incident and tried to rock it as you are now? Have you ever tested the cylinders for slack prior to this or could this be an ongoing situation that has been there for some time and just gone unnoticed as the tractor was doing everything you wanted so you never had a reason to look for this? I can understand the bucket no longer sitting flat on a smooth/ flat surface after smacking a tree with a nice long lever in the grapple, but still think the cocked bucket and the cylinder slack are two different issues.
Just to be clear, I'm also thinking that the two issues are separate, but not convinced that the rocking of the bucket is a problem. The OP says he always lets the pressure out of the system completely when he shuts it down. And he also says it works and lifts fine.
I always did the same release of pressure with my first little compact tractor. Unfortunately, my time machine isn't working either, so like the OP I cannot say with absolute certainty that the rocking is normal, but I think it is. I think I remember doing that same move. Several other posters back on page one said the same thing. Billrog says all of his tractors do it.
I'm inclined to think that the rocking has nothing to do with the accident, and is entirely normal and if anything is related to how each of us shuts down our tractors and how/if the hydraulics system is depressurized.
The bent whateveritis is a different story. Sorry, but I hate the idea of levering a tractor hard enough to yield anything on the loader arms.....Especially trying to controllably yield a cylindrical shape in torsion. Yes, the loader was probably designed too lightly, but it is still hell for stout. What else might break if he does that?
Here's another idea..... What about just accepting that the arms are slightly different. You can't see it and can't even measure it. So concentrate on fixing the bucket tilt.
What about taking out the welder and adding a quarter inch of metal to the top edge of the left hand SSQA plate where it fits up into the "V" on the bucket? Or grinding that much off the right hand one. Could we make enough difference in those two plates to level out the bucket? If it didn't work, we are out a fairly inexpensive piece of steel. Nothing major.
rScotty