Cap separation

[plusone876]

First of all, I have a 1971 20' SF that I recently put a 2015 150 etec on the back. Great performance so far. I have notice that the cables are really stiff and am going to have them serviced under warranty.

I was washing my boat the other day and noticed some flexing in the hull in the aft portions of the port and starboard sides. I looked under the rub rail and it looks like the cap is starting to separate from the hull. I do not know much about boat building, structure, etc. so I have several questions. How big of an issue is this? Could continued use damage the stringers, liner, etc. by letting water in? What is the best method to fix this? How much would you expect something like this to cost if the work was hired out? Thanks ahead for the responses. Currently, frustrated!