Reef, under the water pump there is a plastic housing that has the upper lower unit seals in it, you can buy a complete pump kit that will have it in it.
After cleaning the area up, pry the seal housing out and install the new one in its place.
The housing already has the seals in it but you may have to select the proper O-ring from the kit on it.
Replace the shift shaft seal while you are at it, it will have to be ordered separately.
Before I forget, clean the drive shaft and lightly grease it and the seals before you install the new housing, and be gentle going over the flat spot where the impeller key goes so you dont wreck the new seals.