PUTZKNECHT S48-3 The best: no problem pumping silicone KREND ,and another material, in three years replaced only one part (cost arround 60£) how long you can use stator and rotor it depends on material and there are different stator/rotor supplyers
http://www.uelzener-ums.de/Prospekte/S48-3eng.pdf
http://www.uelzener-ums.de/Prospekte/S48-3eng.pdf