First make sure your bilge pumps are working properly, because it is the prudent thing to do.

Next clean the area between the shaft seal and the spare seal.

You will need a diver to stuff rags in your stern tube and possibly pull your propeller off, if the shaft will not slide far enough back to replace the seal.

Break the shaft coupling and slide the shaft back enough to either slide a new seal on using the seal protector or to remove the housing from the shaft. If you feel confident enough to remove the housing, it will be easier to replace the lip seal with the housing on the bench.

Find the beveled edge on the retaining ring that is around the lip seal in the Strong Seal housing and push it towards the shaft. Now pull out on it gently and unwind it 2 times around. You will have to remove this from the shaft in order to slide the new seal into place.

Take a hook and pull the existing lip seal out of the housing or drill a small hole and place a self tapping screw into the existing lip seal, keeping in mind that it is ONLY 1/2" wide and use pliers to pull the lip seal out.

Clean the Lip Seal pocket and insert the new lip seal into the pocket.

If the housing is still mounted on the stern tube, it would help if you could brace the housing of the StrongSeal using some wood or other means but DO NOT put it against the Water Injection Fittings, as they will snap off. This keeps the hose from compressing when you are pressing the lip seal into place.

Using a Hammer and a flat piece of material, smack the seal into place hitting the flat material on all sides so as to press the seal in evenly. Once the Lip Seal is flush with the front of the housing, use the appropriate tool to press the lip seal the rest of the way in and then reinstall the retaining ring.