Rebuild kits are (or at least were at one time) available for the water pumps from Mercedes. A special puller was required to get the impeller off, one that grabs the entire circumference to prevent breaking of the impeller.

Not a job that is worth attempting by the time you buy the seal kit and replace the bearing/shaft assembly.

Cast is on the left. Cast is literally molten metal poured into a mold, which looks thick and rough. Stamped is a flat piece of metal that has the corners bent up to form the blades, which is thinner and smoother.

-Rog

When a new pump is available from multiple sources for $50-60. even the idea of rebuilding is a non-starter. Google & Ebay are your friends.