Cabriolet hood problem

I have a problem with the hood, the car is affected by the temperature outside, when the hood and the metal is warm ie the temperature is above 22 degrees the hood works perfectly. when the temperature drops and the car is cold the hood struggles to open. I have replaced the 5th bow, the main hood open switch, I have also replaced the ECU several times and I have replaced several time the hydraulic pump, and still I have the same results. As I said the temperature affects the working of the hood, If I put a hot hairdryer in the boot for 10 minutes the hood works again, the hairdryer is directed to the side where the ECU the pump is and further up from this is the outer right roof ram with sensors Can anyone help with this issue please

What year is your 9-3? Not sure what forum to move this to as it could be the 1st or second generation 9-3.

Have you checked the hydraulic oil level for the pump?