I am no expert either by any-means but just repeating what i read. If you want more info on the subject just due a search on toe in toe out and there will be plenty to read. I have been changing my sea water pump housings and impellers after 3 seasons of use on this boat and my 29 enticer I had prior. I have been doing these intervals for the last 13 years with no failures during the 3 seasons of use before changing. I did have one go bad on me years ago when I started on the 5th season on the same impeller, after that I go 3 with no problems and they still look decent when I replace them. They do sit in anti-freeze over the winter which probably helps them stay lubricated for the first spring start up. I think a lot of it has to do with what kind of water you boat in, if you are always in shallow water sucking up sand or tiny stones it probably shortens there life a lot.