All the following could contribute to excessive oil consumption in an engine EXCEPT?

Excessive oil consumption in an engine typically results from conditions that allow oil to enter the combustion chamber or escape from the lubrication system. Worn valve guides, tapered cylinder walls, and worn piston rings are all issues that directly lead to oil finding its way into the combustion process, thereby increasing oil consumption.

Worn valve guides can allow oil to seep down the guides into the combustion chamber when the engine is running, leading to increased oil consumption due to oil burning along with the fuel. Similarly, tapered cylinder walls can create gaps that allow oil to bypass the piston rings and enter the combustion area. Worn piston rings compromise the seal between the piston and cylinder wall, allowing oil to leak past and burn with the fuel.

In contrast, a leaky oil pan gasket primarily allows oil to leak out of the engine rather than affecting how much oil is consumed during combustion. While a leaky gasket can lead to a decrease in oil levels over time, it does not directly contribute to excessive consumption of oil during the combustion process.