Having just put a run-aground 19 skier back on the water last month, looking for leaks is fresh on my mind. What I would do is remove all access covers, etc, so you can see all the likely areas for water intrusion, and then take the boat out with an assistant/co-driver so you have a chance to view the areas while at speed. I mean it could be leaking mufflers, leaking exhaust hose, leaking shaft seal, leaks around the shaft log, etc. It should be obvious though. Your helper is key -- have him/her drive while you look for the leak, or vice versa lol.
On mine we had to do some glass repair around the shaft log area -- my guess is that it flexed it when the boat was run aground (before I purchased it) and opened up some small cracks.
Of course the prop strike damage on the bottom of the hull had to be repaired too, but that was not the source of the leakage.
If your rub rail is where mine is, I think it would be unlikely as a source for your leak -- too high up on the hull, and not exposed to enough water during normal running.
1984 Stars and Stripes Powerslot
White with blue stripes. purchased 9/2012