Dave,
As I mentioned, my Sherwood pump failed 3 years ago and I replaced it with Seaboard Marine's SeaMax pump. Better design, better quality, with a splined shaft that makes inserting impeller easier, and a threaded impeller face with a removal bolt that comes with the new impellers. The cramped placement of these pumps on Cummins engines are always an issue. My engine doesn't have an aftercooler, and the hose coming off the pump feeds the fuel cooler. I remove that hose to the cooler just to give me more room to remove and insert the impeller. In fact, Seaboard Marine recommends removing the fuel cooler, considered a vistigual component in 99% of engine installs.
For those responding about removing the pump for impeller replacement, the Cummins gear-driven pump installating doesn't accomodate that. Access to the pump attachment bolts are blocked by port side, front motor mount (and other plumbing), and that pump removal requires jacking that point of the engine slightly to remove that foward motor mount. There are some Cummins engines that have a belt-driven raw water pump which can be easily removed.