The O-ring in the Y pipe would have nothing to do with loosing PS fluid. If you get a water leak only while the motor is running, I would think the Y pipe may have a crack or hole up higher. If it was down lower where it connects, it would leak all the time
Drive showers are good if there is enough power and/or your running long distances. Don't think doing anything to the original gears will help, just my opinion. Just be easy taking off, don't drop the hammer, either that or switch to a Bravo drive
The PS pump for a car is the same, but the pressure valve which screws into the back and the one line attaches to is what makes the difference. Keep the old one and use the new pump