The C&C 30 Mark I is a wonderful boat, I owned a '77 for a number of years and I would buy it back in a minute. Craziing around the stanchions would not be unusual on most any boat of that age, and would not be a sign of weakness, nor increase the risk of a wet core. So ignore that concern and move on...
To the general concern that ANY older boat could have areas of wet decks from aged or improper bedded fittings. 99% of the boats you will look at will have balsa-cored decks, where testing for wet decks is one of the many reasons you hire a competent survey.
$12k for a C&C 30 would be a lot of boat for little money, I would expect the boat to need some work or upgrades as models of that age typically list for twice that price. So don't expect perfection, you are buying onto a quality boat at a budget price, there'll be reasons why.
Certified...in several regards...