Interesting: https://ntrs.nasa.gov/citations/19950008234 https://ntrs.nasa.gov/citations/19950008234 "Liquid oxygen is [the high pressure oxidizer turbopump's]

Interesting: https://ntrs.nasa.gov/citations/19950008234 https://ntrs.nasa.gov/citations/19950008234 "Liquid oxygen is [the high pressure oxidizer turbopump's] only lubricant and a poor one at that." So it's some lubricant and I imagine also significantly a coolant. This https://ntrs.nasa.gov/citations/20100023061 https://ntrs.nasa.gov/citations/20100023061 goes into a lot more detail. But exotic materials and designs bathed in LOX which provides cooling (and minimal lubrication) seems to be how the space shuttle engines achieved their long bearing lifetimes.