I ve had the same problem on a couple of them.The nut thats in the plastic housing is spinning. I put a socket on my drill to spin it fast, it melts the plastic so the nut will pull out with the bolt. Then I put a different bolt back with a nut on the back of the rear cover. Luckily my bolts were on the top so they were easy to get to the back of to put a nut. now I put anti seize on the bolts so hopefully the want seize up.