Yes there are a number of springs, and tiny little steel balls in the valve body that can cause problems if they're broken or messed with. I did a valve body rebuilt once. It's doable but not fun. If I had to do it again I would take my chances with a JY valve body.
https://imgur.com/a/8X4RT75
https://youtu.be/LdF5DnGwz7E
On my other car (E320) I ended up replacing the torque converter lock up solenoid to cure harsh shifts. My foxwell nt520 has a diagnostic mode hidden in one of the menus that lets you shut off the torque converter lock up solenoid. When I did that, super smooth shifts. TQ solenoid is most likely to fail because it's used in every gear. I suspect nt510 can also do that.