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.

Remove the 2 (or 4) screws that hold the Spare Seal Carrier together and set them and the carrier shells aside. Do not lose these parts as they are re-usable

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 place a self tapping screw into the existing lip seal, keeping in mind that it is ONLY 1/2"  (12mm) wide and use pliers to pull the lip seal out.

You will have some water coming in from the outside, but it should only be a few gallons at most.

Clean the Lip Seal pocket and push the new lip seal up to the pocket.

Reassemble the Spare Seal Carrier on to the propeller shaft making sure that the shouldered side is now facing the lip seal. This is the tool that you will use to seat the lip seal into the housing.

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, tap the seal into place by hitting the spare seal carrier on all sides so as to press the seal in evenly. Once the Spare Seal Carrier is flush with the front of the housing, reinstall the retaining ring.

Remove and store the Spare Seal Carrier unless there is a second seal, otherwise re-install it with the shoulder facing the transmission coupler. Make sure you leave at least 1" (25mm) of space between the shaft seal housing and the spare seal carrier.