before you start tearing into it plug everything and see if it still happens.
Plug everything at the transom, plug the drains at both ends, plug everything you can. Remove one plug at a time and wait for however long it would normally take to get the water in the bilge.
Plugs are cheap and easy, see if you can narrow it down to one line and fitting.
I found that I could put a piece of paper in my lines and it would be dry at the end of a trip, but my bilge was still swimming, so I replaced all the thru hulls, same issue. So I dried everything mounted a go pro to watch the bilge and the water came from the front, hull issues...
I thought I would provide an update to this thread because the leak has stopped. And my "strategy" was to do absolutely nothing. For whatever reason the bilge has been dry as a bone the last half dozen or so trips on the lake and I have zero idea as to why this might be. Maybe I will write a letter to the Vatican to see if this qualifies as a miracle.
That is ridiculous! After all those years. Maybe there's a thirsty mouse living beneath the deck and he's drinking it as it comes in?