You will probably break the threaded inserts out from the plastic to get them loose. There is a TSB about this with a part number so that you don't have to replace everything shown in the parts catalog. When you put it back together, use anti-sieze on the new bolts so that they won't corrode next time.
Anyone else out there that can still get the bolts to turn that hasn't put some anti-sieze on them yet, do it now so you won't be sorry later.