I doubt that a leak in the pylon could account for that much water. There is also an intended vent built into the pylons. Usually the forward ones.

I would look at the hull bottom, keel for wear and a possible leak. That is a ton of water!

You can seal the pylon by coating the top of the foam with silicone. If you don't want to pound the boat apart to get at the top of the post / foam you could inject 2 part floatation foam into the bolt hole.