I have a 1991 Hunter 30. I need to replace ? or add packing to the drive shaft exiting the boat bottom. Can I do this while the boat is in the water or does it have to be lifted out of the water first. The installation that came on my boat has a white plastic nut that can be tightened down to stop water flow. I usually tighten this nut by hand when I leave my boat so no water is leaking in at all. The distance between the fixed white nut which is towards the rear of the boat and the compression side white plastic nut is growing smaller now. I have noticed that when I run the engine now that a lot more water seems to be leaking in past the nuts. Any ideas on what kind of packing is the best ?Thanks for your help.Larry