[Sans Peur]

Measure the actuator fully closed and (assuming it isn t working) disconnect it from the window mount and open the window as far as it normally would be and measure the distance from closed to open. That will give you the approximate travel of the actuator.

Go online and Google Thompson linear actuators. You will find a ton of suppliers and can look at the specs on them. You don't need one with a heavy lift capacity. They will have them listed by length, travel distance , voltage, shaft diameter and lifting capacity.