Lubricating oil contamination in a gas turbine bearing oil sump will most likely come from which of the following?

Correct Answer: Option D — Failure of seal pressurization air.

Bearing sumps utilize pressurized air to maintain a positive pressure differential across labyrinth seals, preventing oil leakage. If this seal pressurization air fails, the pressure gradient reverses, allowing hot, contaminated gas path air or combustion byproducts to enter the sump, rapidly degrading the lubricating oil and causing bearing damage.