I remove and inspect mine once or twice a year. When reinstalling I grease the housing, shaft and end plate with water proof grease (per old manuals). At 5 years I replace them and keep as emergency spares.
The grease really helps drawing water on the first start and keeps from burning the impeller in a dry housing. When I worked in yards and owned a yard, I noticed others impellers were often ok in the middle, but the ends were cracked and hard. I assumed it was from running dry. It's how my dad (Chief Engineer) taught me. I only found the passage in an old manual a few years ago. All old geezers I know grease their impeller housing.
Works on current pair of Detroits, Onan and Perkins generators and every engine I've owned or maintained.