You can use boundary layer lubrication, just need a high enough pressure fluid ( anything including a gas under high pressure) that will form a film between metal to metal contact, and then have a backup system, either a solid lubricant like PTFE or molybdenum sulphide to handle the start up and shut down conditions of low pressure, and of course you can also use bearings of some sort with the same lubrication regime. At the speeds the pumps operate at this would be enough just having a small scroll on the shafts both sides of the seals and putting in the liquid to make them both self priming and self maintaining. That it is at 3K is not really much difference than if it was long chain carbon molecules at room temperature, your choices of materials just get a little more expensive and exotic.