How can over-tightening fittings increase the risk of corrosion on a boat?

When fittings are over-tightened, it can lead to cracking in protective coatings, which is crucial for preventing corrosion. These coatings serve as a barrier against moisture and environmental elements that can promote oxidation and corrosion of metal surfaces. Once these coatings are compromised, the underlying metal becomes exposed to the elements, increasing the risk of corrosion.

The other choices do touch on important aspects of fitting maintenance and integrity, but they do not directly address how over-tightening specifically leads to an increased risk of corrosion. For example, while proper sealing and the ability to remove fittings are important, they do not directly relate to the corrosion process in the same way that damaged protective coatings do. Additionally, only some leaks may arise due to over-tightening, which could be a consequence rather than a direct cause of corrosion risk. Therefore, the crux of the issue lies in the damage to protective coatings leading to exposed metal.