I had the hardest time looking for various leaks on my Hunter 23.
First Source
Some leaks were the sliding entry hatch on the top when we got "gully washers". You can tell by various wet spots afterward on upholstery, standing water or watching the drips with an internet camera inside the hunter cabin during a big rain storm. A lighted cabin with an interior internet camera permits. On my dock I have wireless service with an Amazon Show placed inside with a worklight controlled by Alexa, So when the storm starts, I grab a beer and start watching from the house.
The fix
I basically put foam weather stripping at some locations on the hatch pieces to divert water during heavy downpours. Also, I raised the Sunbrella hatch cover with a 2X4 laid on its edge above the hatch to encourage shedding and non-pooling of water on the hatch cover during a hard downpour. A review with the internet camera during big storms validated success. Every time I close the hatch up I place the board under the Sunbrella to make a small tent like structure and wait for the rain.
Sponging on the pocket compartments under the floor boards and the use of a wet dry vacuum on the weep holes in those compartments helps clear the water in the inner hull and dries the interior for the next experiment.
Second Source
The most sinister place for leaks was the joint match between the hull and the top part of the hunter. The rub rail tended to collect water and feed it into the interface gap. The water would run down behind the top edge of the rub rail holder and collect behind the rub rails, instead of draining out the bottom of the rub rail holder. The water would build up and enter the interface between the hull and the top of the boat and then run down the inside of the hull and pool down below
Depending on how the boat was listing the water would accumulate behind the rub rail along the side and enter inside at a spot least expected. I had put on a new rub rail and holder which contributed to the problem.
The fix
I put silicone along the top edge of the rub rail holder between the holder and the hull and drilled some tiny holes on the bottom of the rub rail holder along the side of the boat. The trail of water seeping though the drilled holes, particularly at the stern of the boat informed me that water was accumulating there and seeping inside through the interface between the bottom and top boat halves. Towards the back of the boat (lowest elevation of the boat top and bottom halves), I put some clear silicone at the interface on the inside to encourage the water to stay on the outside.
After doing these fixes, it has been very dry interior in my Hunter 23 (many Florida downpours have occurred). It just takes time, patience and trial and error.