same happend to me dude. tried to lever the plastic off but becuase the rust had warped the metal a bit it snapped. i just then sanded it down back to metal, applied anti rust stuff and then primed it and sprayed, carefully puttin newspaper and stuff around to stop paint gettin all over the place!! its a tricky bit to do and the most annoying becuase of the shape of it.
im sure yours was bubbly like mine. pain up the ass.....