On attempting to lower my '02 cabriolet roof, the front of the roof releases and rises approx 3-4cm then stops and will not go up or down. This started as a very occasional problem but now happens most times when trying to lower roof. You can then repeatedly attempt to lower or resecure the roof without success for up to 15mins, with or without the engine running. It will however eventually lower and will always close from the fully open position without problem. Dealer recommended replacing battery. No difference. They now want to replace the pump (very expensive). Anyone else had this problem?