I don't think the flex is caused by deteriorated core material, when someone steps off the dock onto the gunnel it slightly tilts down, there are no apparent soft spots or problem area it apears that all my boats gunnel support comes from the connection where the cap meets the hull. I'm sure that if i removed the cap and replaced the core then reglassed it and added extra support/glass it would be stronger and probably would not flex but that seems like alot of work that I think (correct me please if I'm wrong) could be avoided by replacing the original or installing new brackets.