When Replacing Pump Seals, Keep it Clean
The biggest trick with replacing pump seals is to keep everything clean.
Never touch the faces of the new pump seal or the seal ring. Just the oil from your skin is enough to mess up pump seal.
Take the pump housing apart and remove the old pump seal. Clean the pump shaft seal mounting surfaces with a fine emery cloth. Then wipe everything down with a clean lint-free towel.
I put a tiny dab of clear silicone or RTV silicone on the mounting surfaces before I press the seal into the hole.
Put a piece of paper over the seal face to protect it and use the handle of a screwdriver to carefully push the pump seal flat into the hole.
Make sure the face is perfectly flat and parallel to the motor shaft.
Remember: Keep it clean. Don't let any silcone squirt onto the face of the seal.
Drop the rest of the seal kit into place and tighten down the impeller on the shaft.
Never run a pump dry. Don't even spin the shaft by hand until the pump has water in it.