This video shows how to disassemble and reassemble the low range 10 kPa/kg piston-cylinder. The process is similar to that used for the 20 and 50 kPa/kg piston-cylinders.
See this article for part numbers and ordering information for o-rings, tools, lubricants;
PG7000 Spare Parts & Tools; O-rings, Gloves, Lubricant, Fluids