Aftermarket parts

Many years ago, I had the same issue with the stove vent. It was cheap plastic and even worse the hinge was a 1/4" x 1/8" projection at each end that fit into holes to allow the flap to pivot. Those projections broke with almost no use.

I stopped by the manufacturer and complained about that item. The offered me two choices for replacement. The first choice was another piece of junk identical to the one that broke. The other was similar junk except that a piece of tape allowed the flap to open and close. Clearly that was not going to work either. I went with the original style and when it broke I replaced the plastic pivots with a coat hanger.

It hardly makes any difference. The vent flaps when driving unless to plastic toggles are moved to the closed position. That constant flapping would break even a well made vent. The toggles are so high that I need a stool or step ladder to reach them. Hence I rarely use the vent. Instead I just use the Fantastic fan in the ceiling.

If you notice, a lot of RV parts are similar junk. The manufacturers often don't have decent parts to use either.