An integrated pressurized pump shaft seal assembly for a rotary fluid pump is disclosed. The seal assembly may include an oil reservoir; an integrated centrifugal oil pump directly attached to and rotatable by a pump shaft and fluidly connected to receive oil from the oil reservoir; a seal chamber fluidly connected to receive pressurized oil from the centrifugal oil pump and comprising: a pump shaft bearing adapted to be lubricated by said oil, and a mechanical shaft seal surrounding the pump shaft and adapted to seal the seal chamber against ingress of a pumped fluid. The integrated pressurized pump shaft seal assembly may also use first and second mechanical shaft seals. A rotary fluid pump including a pump motor, pump shaft, pump impeller assembly and integrated pressurized pump shaft seal assembly is disclosed. A method of preventing seal failure in a rotary fluid pump is also disclosed.