How to tell if hollow stringers are bad? 20' 1969

[Bigshrimpin]

Make sure you inspect all the through hull fitting especially the scuppers that go down through the floor. And there's usually a block of wood b/w the deck and the bottom of the hull. This one leaked on me . . . about 8 gallons an hour

Also on my 18, I had the bronze thru hull in the front fish box come loose half way across cape cod bay (10 miles from shore) . . . I had to plow home at 8knots with the bow in the air.