Jon:
I can't be sure that you are seeing "stress cracks" verses gel coat cracks. Pygmalion has cracks like this in several places near the mast and also NOT near the mast. Some are small - others large/long etc. I other words I'm not sure that you are seeing more then gel coat cracks - usually considered unsightly but no uncommon with boats of this age.
IMHO you need to check that the support under the deck and below the mast downward to a block that sits on the hull is secure and NOT being compressed. Sometimes the block under the cabin sole becomes soft and is compressed by the load above. ( and sometimes the block is not even there.)
One way to check for sagging beam is to sight along the bottom of all the cabin beams - they are supposed to be the same arc and should align along the bottom.
Also the beam under the tabernacle is NOT a solid piece (usually) - it is made of multiple pieces that enclose the bulkhead - not a great design load wise.
Below is an image of the beam and support.. the black metal c section is my latest attempt to correct the poor design of this area by spreading the load.
The album with more images on picasa.