prop spins in neutral

so hears the deal, the boat is an 86 sn2001. the transmission is original. motor is a 351w with 900 hours. the prop is spinning in neutral and has been for a season. i have just dealt with it without any problems. well now i need to take the boat in to have the carb tuned up and that means they are gonna use a fake a lake process to do it. ive heard its bad to have the prop spin out of the water. so i guess this means i need to get this little problem solved. i called the nautique dealership and they said there are these "packs" in the transmission that are designed to wear out and thats what the problem is. the problem with that is they want a 600 dollars in labor to get the packs switched out. does anyone know anything about this? is this even the problem? can i switch these packs myself? oh yeah and i know its not the idle speed, the idle speed is dead on. thanks for your help in advance