Final answer:
The least likely occurrence when a radiator pressure cap gasket or filler neck seat is damaged is that the lower radiator hose will burst. This is less likely to be a direct result of the pressure issue compared to boiling and overflowing of the coolant, or engine overheating.
Step-by-step explanation:
If either the radiator pressure cap sealing gasket or the radiator filler neck seat are damaged, the least likely outcome is that the lower radiator hose will burst. When these components fail, it typically means that the cooling system will not be able to maintain the proper pressure. As a result, the boiling point of the coolant is reduced, and it may boil sooner than it should, potentially causing the engine coolant to overflow and the engine to overheat.
However, the pressure failure due to a bad cap or damaged neck seat is less likely to directly cause a lower radiator hose to burst compared to other causes, such as a hose defect or external damage.
If either the radiator pressure cap sealing gasket or the radiator filler neck seat are damaged, the engine coolant is more likely to overflow rather than the other options listed. When the pressure cap or the seat is damaged, it creates an opening for the coolant to leak out, resulting in overflow. The lower radiator hose bursting, engine coolant boiling, and the engine overheating are all possible consequences of a damaged radiator pressure cap or filler neck seat, but they are not specifically the least likely to occur in this scenario.