What are some common causes for external oil leaks?

High crankcase pressure or gasket leaks can indeed lead to external oil leaks in a variety of engines. When the crankcase pressure increases due to poor ventilation or excessive blow-by from worn piston rings, it can force oil out through seals and gaskets. Additionally, gaskets that have aged or been improperly installed may crack or break down, creating points where oil can escape. This option encompasses a wider range of issues than just one specific cause, reflecting the complexity of potential sources of oil leaks in an engine.

The other choices do not represent common causes for external oil leaks as effectively. Focusing solely on oil filter leaks overlooks many other potential leak sources. Low oil level warnings indicate a problem but do not directly cause leaks themselves. Oil viscosity changes may affect how an engine operates but are not a direct cause of leaks. These factors contribute to engine health, yet they do not directly correlate with the occurrence of oil leaking externally.