M_Boats: Hull to deck joint

We've got an old 1974 M17 that I bought for a song (well, for the price of a decent guitar), and it's going to need a lot of work.  Most of the work will be cosmetic, but when I got her she was full of water, and I'm wondering if all that water came in through the hatch and companionway, or if the hull/deck joint is susceptible to leaks.  I'm not sure how the joint is constructed, or if I ought to pull and re-bed the toerails.  Or if the boat will pop apart if I remove the toerails!  Any thoughts about what I might want to look or watch out for before I put her in the water?