To be clear.....we ate talking about curl cylinders right?
What prompted you to rebuild the last time?
Do you have quick connect hoses on the loader?
If they are indeed the curl cylinders, the problem can either be the cylinder OR the valve.
If you have quick connects, put a jack under the bucket to take a little pressure off.....the unhook disconnects.
If bucket still dumps, problem is in the cylinder. If the drift stops when unhooked, it's the valve