My experience with those (Challenger) is that it was a bear to get off for a start. Despite taking care (clearly not enough...) it flew off at speed and hit the floor and over to my car 8 feet away - could easily have hurt me or chipped the car, broke a window etc.....care is required.

Once cleaned I tried to reinstall and no matter what I did I could not get the required one revolution+ on the spring. I tried channel locks and a bunch of other stuff. It eventually bent the spring tang due to the force required to try and reinstall. Maybe Challenger springs are stronger due to the large window.

I actually ended up buying another complete regulator because even if I got the spring back on I did NOT want that bent back tang breaking off and releasing that energy inside my door.

Lesson learned! Be careful!