Which of the following is a common cause of an oil leak in an engine?

Worn gaskets and seals are a common cause of oil leaks in an engine because they are critical components that create a seal between various parts of the engine. Over time and with exposure to heat and pressure, these gaskets and seals can deteriorate, crack, or become misshaped, leading to oil seeping out from the engine assembly. Since the oil system operates under pressure, any degradation in these components can directly result in oil leaking out of the engine, which can compromise lubrication, lead to low oil levels, and potentially cause engine damage if not addressed promptly.

The other options, while relating to engine performance or integrity, do not directly cause oil leaks in the same manner. For instance, a dirty oil filter can lead to restricted oil flow or poor filtration, but it doesn’t typically result in oil leaking out of the engine. An overfilled oil reservoir can cause foaming or excessive pressure that may lead to some leaks, but it is not as common as the deterioration of gaskets and seals. High coolant levels pertain to cooling system issues and don't contribute to oil leaks. Thus, worn gaskets and seals stand out as the most direct and frequent cause of oil leaks in an engine.