I cut a new shaft from some stock stainless steel rod slightly oversized, drilled the cast to fit for easy but tight movement, ran the bit through the flap, hacksawed a slot in the rod for the thermal spring, drilled and tapped the flap and rod for a small stainless screw and peened the end after put in place. i added a little more length to the slot end of the rod to not need a spring retainer.

Larry
Old man᠁Old truck᠁neither one goes very fast. All you need in life is TIME, PATIENCE and MONEY.
If you are missing one component, you'll need an abundance of the others two.