Do you know the age of the raw water impellers? They should be changed every 2 years. Also bellows should be inspected for signs of cracking in between the folds, leakage can result in damage to the gimbal bearing and u-joints and even sinking.
Are you familiar with outdrives and their maintaince?
1997 Silverton 362, 7.4 Crusaders
1997 2400 SCR, 5.7 Vortec / Bravo 2