Ortega Check Valve Rattling and Leaking

My raised spa level has been going down each night and I think I've narrowed the problem down to an Ortega check valve in the return line. Also, when I allow a full flow of water in the spa line, which is shared with the pool return, the check valve rattles very loudly. I've lubed the insert but that has not helped. I would order the insert part for the valve but the current one looks fine with no warping or other damage.

Has anyone seen these problems and solved them by replacing the seat assembly insert? Thanks!

--Dave