Hi the rear offside door of my Astra will not open as normal, as though the central locking is still engaged, I managed to open it by using the inside lever, while the C/L was engaged, but not otherwise, I assume that the solenoid has failed and needs replacing, do I need to replace the complete unit?. while the door is open, and I use the key pad I can hear the lock operating, my pet hate with car diy is removing trim, I always finish with a load of broken clips etc. any ideas please