Hey Bill,
The crazing you are noticing is probably from water trapped in the hull freezing this winter. If there is water in the hull you can do another cheap check. When the temperature is below zero can you notice frost and or condensation forming on the hull in the "wet" areas...it is the water in the hull cooling that area...I noticed this on the last boat I owned. Every spring I would notice more condensation around the areas that had water. I then knew I had a problem, tapped with the hammer and started another project.
Is this area you are concerned about around the exhaust? I was lucking on my J/30...the exhaust issue was resolved about 10 years ago so the hull below the water line is dry.
