you are right, if the tolerances are very unfavorable, it is possible that the swivel arm can’t move.
So please make one of the following changes, you can chose which one is easier to realize in your workshop:
make new tubes (part 622) with L=15,6mm (instead of 15,3mm). The general tolerance of +-0.2mm is o.k. or
machine the part 604 to 14,7 +-0,15 instead of 15 +-0,15. Paint primer according to VN1454 to the re-machined surfaces.
Please tell me which way you have chosen and if the swivel arm moves after making this changing.
In future I will change the drawing of part 604 to 14,7 +-0,15.
Regarding the O-ring we can’t do anything for Zoucheng because we can’t change the casted parts.
I will check if a wall thickness of 11mm instead of 9mm is possible, because the space is needed to manufacture the sliding surfaces (not painted) by the milling tool.