A submersible well pump assembly, comprising: a rotary pump; a motor for driving the pump; a seal section (11, 77) coupled between the motor and the pump, comprising: a cylindrical housing having a longitudinal axis, an upper adapter and a lower adapter; a shaft extending axially through the housing, the upper adapter and the lower adapter for transmitting rotation from the motor to the pump; a guide tube surrounding the shaft and extending between the upper and lower adapters; a flexible member surrounding the guide tube, having an upper end sealed to the upper adapter and a lower end sealed to the lower adapter, defining a lubricant chamber between the guide tube and the flexible member and a well fluid chamber between the flexible member and the housing; the housing having a well fluid passage for communicating well fluid to the well fluid chamber to apply a hydrostatic force to the flexible member corresponding to a hydrostatic force of the well fluid; characterised by at least one guide tube passage extending axially within the guide tube between an interior and an exterior of the guide tube from an upper portion to a lower portion of the guide tube; an upper portion of the guide tube passage being in fluid communication with lubricant in the lubricant chamber; and a lower lubricant communication passage in the lower adapter in fluid communication with a lower portion of the guide tube passage for communicating lubricant in the motor with the lubricant chamber via the guide tube passage, wherein any well fluid encroaching into the lubricant chamber must flow down the guide tube passage in order to reach the motor. a rotary pump; a motor for driving the pump; a seal section (11, 77) coupled between the motor and the pump, comprising: a cylindrical housing having a longitudinal axis, an upper adapter and a lower adapter; a shaft extending axially through the housing, the upper adapter and the lower adapter for transmitting rotation from the motor to the pump; a guide tube surrounding the shaft and extending between the upper and lower adapters; a flexible member surrounding the guide tube, having an upper end sealed to the upper adapter and a lower end sealed to the lower adapter, defining a lubricant chamber between the guide tube and the flexible member and a well fluid chamber between the flexible member and the housing; the housing having a well fluid passage for communicating well fluid to the well fluid chamber to apply a hydrostatic force to the flexible member corresponding to a hydrostatic force of the well fluid; characterised by at least one guide tube passage extending axially within the guide tube between an interior and an exterior of the guide tube from an upper portion to a lower portion of the guide tube; an upper portion of the guide tube passage being in fluid communication with lubricant in the lubricant chamber; and a lower lubricant communication passage in the lower adapter in fluid communication with a lower portion of the guide tube passage for communicating lubricant in the motor with the lubricant chamber via the guide tube passage, wherein any well fluid encroaching into the lubricant chamber must flow down the guide tube passage in order to reach the motor. a cylindrical housing having a longitudinal axis, an upper adapter and a lower adapter; a shaft extending axially through the housing, the upper adapter and the lower adapter for transmitting rotation from the motor to the pump; a guide tube surrounding the shaft and extending between the upper and lower adapters; a flexible member surrounding the guide tube, having an upper end sealed to the upper adapter and a lower end sealed to the lower adapter, defining a lubricant chamber between the guide tube and the flexible member and a well fluid chamber between the flexible member and the housing; the housing having a well fluid passage for communicating well fluid to the well fluid chamber to apply a hydrostatic force to the flexible member corresponding to a hydrostatic force of the well fluid; characterised by at least one guide tube passage extending axially within the guide tube between an interior and an exterior of the guide tube from an upper portion to a lower portion of the guide tube; an upper portion of the guide tube passage being in fluid communication with lubricant in the lubricant chamber; and a lower lubricant communication passage in the lower adapter in fluid communication with a lower portion of the guide tube passage for communicating lubricant in the motor with the lubricant chamber via the guide tube passage, wherein any well fluid encroaching into the lubricant chamber must flow down the guide tube passage in order to reach the motor.