I think it must be just rusted/weakened lug mountings on the underside of the sunroof, mine tried to pop out till I set it a bit lower, only by a few mm, don't know if it is the old screws snapping, but I replaced my roof with a better s/h one and SS screws, with CAP HEADS, so they don't sieze AGAIN I also used Coppaslip.
Works for me reguarly do over 150 no problems.
tabetha