Hello and Help please!

My 1982 Four Winns I/O 20 foot fiberglass boat has been running
wonderfully this year (I've owned her for 5 years now)... please
excuse the lack of correct terminology in this post as I describe this
sea water leak problem

Just yesterday, I noticed a bunch of water leaking, with some of it
running eventually into the bilge - and the rest just soaking the
'carpeting' I have that is glued to the upper starboard sidewall...

The boat only leaks when it's moving... slow leak at slow speeds, and
fast leak at wide-open throttle... the leak comes from up top, and
'drips and pours' quite furiously downwards... when i inspect behind
and near to this sidewall, i can see the water leaking/pouring off the
shift cable... I said, "hmmm, that's weird, there ain't no seawater in
that shift cable"

I have a thruhull fitting about 2 feet in front of this leak area, on
the same side (starboard) - at the waterline - for my 'livewell' (just
a box with a thruhull - no pumps, etc)

I suspect, maybe, that this thruhull is leaking, and traveling upwards
and backwards (2 feet) thru the 'core' and then pouring out of a seam

Does this sound reasonable?

Has anyone had this kind of leak problem before?

Could there be water in my fiberglass 'core' from this thru hull?
Heck, does my 1982 Four Winns even have a balsa or foam or some-type
core?

Is there someplace else that could be leaking (some seam) rather than
the thru-hull fitting? Can a waterline thru-hull fitting cause a leak
3 feet higher than the waterline? It's quite unusual for me to see
water pouring in and dripping down? I mean, if the thru-hull was
leaking into the boat, there would be puddles on the floor of the boat
and working it's way to the bilge... I can't explain how water would
pour from the top of the sideboard downwards... unless water leaked
into the core and wicked upwards while at speed and found a seam to
escape and drip/pour down...

I hope this made some sense and somebody has a bit of advice

Regards,
Michael