Depending on the model and size, you may want to look into replacing the back cover and seal with a unit from Speedseal. Welcome to Speedseal
It does away with the paper gasket (uses an o-ring), as well as the tiny screws for the back cover, which makes checking and replacing the impeller much easier. That said, I would assume you will need to contact the company with measurements to determine if any of the kits will work. We installed one three years ago and have been very happy with it.