I have an 2004 LT with central Locking. I have frequent problems with the lock on the stingray cover remaining locked, or at least unopenable, even when the central locking is off. I have greased the latch before in case it was that. The only way to get it open is several, and I mean several, attempts at banging my the palm of my hand against it. This only works one in five attempts. I have not been able to open it on this occasion for over a week. Any thoughts ?