My guess is water is running in via a raceway (may just be condensation water and not a leak) and following the conductors connected to those top few breakers to the breaker terminals. Just having a "drip loop" so to speak (conductor droops lower then the breaker terminal) would promote the water to flow to that point and drip off the conductor there, though sealing the raceway would keep condensation minimized in the first place.
The QO breaker in the CH panel - all that is needed for it to work is for the breaker jaw to attach to the bus, foot rail hooks, clamps - those can be bent, broken or removed :happyyes: