i have a 77 75 hp johnson stinger (long shaft) that I need to reseal. just changed lower unit oil and it had some water in it, no visible cracks in the lower unit so i assume it needs reseasled. what kind of money am i looking at for that is it some i should attempt it myself, or let a pro. do? if i did do it i would get a service manual, and change the prop seal, and water pump as well