Plastic does fail overtime especially in heated applications. Your in FL. chances are that boat has seen salt water as well. I wouldn't use that t-bolt, I would use a standard stainless steel radiator hose clamp.
Trust me. I worked professionally for 9 years on exotic cars in miami. I know FL heat, and the majority of repairs I did were on the cooling system.
Cooling systems are now a wear item, just like brakes, tires, belts, oil etc.
Nearly every model uses plastic and the weep, seep, crack, split, burst, overheat everything. Ive seen cars where customer just kept on driving because coolant thermostat housing split, ignored the red light, engine detonating out of control and melted the plastic intake and knock sensors to the cylinder heads lol.
Thermostats usually stick open, causing overcooling, and lower engine operating temps, causing an engine to run in open loop longer, burn more fuel and ecm thinking it is in warmup mode constantly ( thats in the obd2 world, i dont know what these boats run on ) there are instances where t-stats stick closed and then the weakest point in cooling system will blow or begin to bleed off psi, and leak coolant.
You shouldn't have any more problems with it for a while, but why used? They don't offer this item from dealer?
( I mess strictly with 90s 2 stroke seadoos so if this is some unobtanium boat part then don't wonder why I asked if you couldn't purchase new ha )
Rob
