Hi Koricorn, welcome to the forum. I too, have piano hinges that used to leak, but not any more. I found a wonderful caulking compound that comes in a tube. It is called "2 X the stretch", it is clear and available at the big box stores. If you purchase a tube, slip it into your caulking gun and get prepared to solve your leaking problems, once and for all. Simply wire brush the piano hinge to remove all crud and then open the hatch lid, just half way. Apply a liberal amount of the stuff all along the hinge on both sides of the hinge pin area. Run your finger smoothly from end to end along the caulking, allowing it to completely cover the hinge in a smooth, even layer. Leave the hatch lid in this position for 4 or 5 days to let it dry, and then when you close it, it will streach the caulking and when you open it, it will compress the stuff but won't fracture or split.
Give this a try, it has worked well on all 3 of my tears and completely solved the water problem. You've got a great one-of-a-kind original teardrop, what a find. Good luck with your insulation efforts and come on out to So Calif when you make that cross-country trip to break it in. The coffee is always on.

Roly, the So Calif woody guy.