The fenders are a common problem and folks have fixed them in various ways. Those thin metal brackets for support will break once they start flexing a lot. First look over the fenders and see how many screws have pulled through the plastic, cracked it etc. You didn't mention that so maybe they haven't.
I used 8x32 spring nuts on the back of all my screws to retain them. I also put finishing washers under the heads to keep them from pulling through the plastic;
https://www.amazon.com/Hillman-31017...57669433&psc=1
Get the appropriate size for your screws. I painted mine black. I used 1/8 x 1" aluminum stock and fabricated new supports to go behind the fenders. I also used some stock that was a bit thicker in some of the longer, "flexier" spots. As a warning if it crosses your mind; I thought I would use some locktite on the screws into the spring nuts - don't. Melted a perfect circle the size of the screw in the fender.
Others have replaced all the screws with stainless screws, washers and nylock nuts.