I have dissasembled the valve body and found out these two problems:
1) there was no check ball No. 1 (orange check ball) in the valve body. It should be here (on the picture the check ball is on its place - I have just tried it)
however, I found this orange check ball here in the case (I think there should be no check ball at all):
So, where should be this orange check ball? If not in the case - could this cause something bad? (for example burnt direct clutch..)?
2) This spring in the valve body was broken (1-2 accumulator valve). What could cause this?
That ball needs to go where you have it, in the vb, not in the case...make sure it is 5.16 ball and doesn't fit through the hole in the plate.
This ball is not "required" to function, however it will for sure keep the harsh 3-4 4-3 shifts from happeinging
As for the spring, common to break, you can experiment with a spring that is same tension as the one ahead of it, they are identical. This spring is not needed again, however helps control the 1-2 shift.