My NL 5KW has the same pump and I've been using the Johnson impellers that came with the boat, wrapped in a sealed plastic bag. With the original pump I kept having to replace the ceramic seal. According to the log, I got 100, 130 and 140 hrs. out of the three replaced impellers, then replaced the shaft and solved the seal problem. When I moved the unit to a new hatch under the veranda, I rebuilt the whole genset and installed a complete new pump, rebuilt the old one, then pickled it for a spare. So far, zero hours on the recon. At least one Manatee out there is using a March A/C pump in place of the old Johnson unit. I might even consider that but having to replace my own March A/C pump three times in four years with low usage, I don't find it any more reliable than the Johnson.