I was given a 1988 (?) 2 stroke 15 hp yamaha motor, which has a chewed up forward gear, I have located a parts lower unit that has a long crack in it, I want to swap the forward gears, how do I get the pinion gear off the drive shaft and out of the way to get at the forward gear? there looks like a 12mm nut holding on the pinion gear? do I remove this nut then pull the drive shaft? I never have done this before so its all new to me, the gears, dog, etc in the lower unit with the crack all appear to be clean and in good shape, just need some help figuring all this out thanks