Hi - not that I would trust the salesman either, but I'd go as far to say this is common for an older anything. Rain water can seep in around various fittings in the deck, hull joint, whatever. Water can even come down the inside of the mast and find its way to the bilge (rotting the holly sole up there in the process).
Every boat I've owned (J/30, Tanzer 22, Melges 24) just plain collected a bit of rain water.
My J/30 will collect a gallon or so in a few weeks if its been raining.
I guess it doesn't mean that there isn't a bigger problem resulting in water ingress as well as a lot of wet balsa somewhere, but this should turn up in the survey anyway.
Assuming we are not talking about a LOT of water, I would not worry about it. Maybe tell the surveyor to keep an eye out for something along these lines.
Good luck with the J! You will find this forum is an amazing resource for these aging boats.
-djm
