Some fitting may be required.
Try swapping the sight cover for the chinese version.
The sight cover has a small indent running across, just below the aperture. This puts tension downward on the sight base and aperture. There are specific techniques to modify/fit rear sight parts to any given receiver. Hard to explain here however.
I have found that stoning, not filing or dremelling, a few thou or so from the front leading edge of the sight cover can ease instal and function on the really tight rear sight installs.