Symphony’s advice is absolutely spot on, the aluminium plates that are bonded into the glass fibre frequently corrode in favour of the stainless securing bolts in such a way that they are gripped so tightly that they will break off rather than undo. Using brute force to remove the bolts will have you wishing that you hadn’t started that day. So if they don’t undo very easily with only gentle amounts of force you will need a lot of patience and some easing oil to flood the bolt and come back in a day or two when the oil has had chance to work its magic. indeed it may be best to soak with easing oil every bolt you intend to undo several days before you start the job.
Good luck, and don’t forget the anticorrosion paste/sealant when you put the new bolts back in place. Don’t use the old ones as they may have been weakened during removal.