If you do decide to reseal, a normal tube of fast drying caulk would work fine. You just have to make sure it sits for a couple of days in the sun to make sure its non-toxic when you add fish. (Basically make sure its Cured). Also wouldnt hurt to run water in it for a week afterwards, just to make sure.
What i did with my old tank was took a box cutter, carefully removed the old caulking, got the gun, and caulked along the edges. Then, wearing a plastic glove, i gently ran my finger along the caulk to smooth it out and make sure it is in place. It may be a little difficult at first, but gets better as you go. If done right, it goes pretty quickly and will hold water fo a loooong time after.