Check the locker on the starboard side aft cockpit. There is a water spigot in there, make shure its turned off. There are screws that you can take out and check behind it and check for leaks on the backside of the carpeted board that the spigot and fresh water inlet are mounted to hope this helps
I had a vibration at 2500 in nuetral. I found that the starboard engines motor mount had worked its way loose. The lower nut backed off all the way down. I brought the nut back up and tightened and problem solved. hopefullyit didnt mess up the shaft