I was out the other day on an older 25' checkmate, we were out for maybe 2 hours and when we came in and pulled the drain plug a ton of water spilled out.. it wasn't rough out and normally nothing comes out. its got a big block bravo one, and he meticulously maintains it and barely uses it...

where could it be coming in from?
and
how do you check, besides dropping it in the water?

check all hose connections and thru hull fittings first. if you dont find the leak you may have to run it with the hatch off or barely open and watch where its coming from.

I would check the drive bellows first. If good then run it on the hose and look for the obvious. If nothing then drop it in the water and climb in the bilge like a monkey!

Check the engine block drain plugs, especially if there the plastic wing nut style.

mine had a shift cable boot split and leak...

Look for cracks.

Another question is why aren't your automatic bilge pumps working?

What I want to know is how you can resist opening the engine hatch for peeking purposes when you get back to the dock. I can't help but look. Maybe I have OCD.

Another idea on an older boat like that is exhaust manifold leaks. No symptoms on the intake side, runs normal temp... some water not making it back in the lake? I have started looking at exhaust manifolds as regular replacement items.

Bellows is my next guess.

And if you check all that and cant find it,,,, its the steer shaft seal.

Hot water or cold?