Newbie Maristar 230 VRS owner
Congrats on the new boat. I have a 225VRS and had the exact same problem you are having. I paid the dealer to look at it and had it repacked and the shaft aligned but to no avail. Digging into it myself while on the lake, I found three areas i was taking on water. The first and biggest area was a warm water shower the previous owner installed. Each time the boat was above 2000 rpm's, it would trickle out of the connection located behind the rear deck, by the air vents. The second area was when we would let off of the throttle, we were allowing the water to pour up over the rear deck and flood onto the vents for the motor. The third area which is not as bad but does leak is the boat rub around he boat.
Another place I would check is your water pump and cooling lines.