To me, fixing seam leaks always ends up feeling like playing a game of Whack-a-Mole. You get one set of bubbles to stop, and then find another leak further down the line. If it has seam leaks, I'd skip it, unless of course, your friend only wants to paddle for a couple hours at a time.
That said, my boat, an 18' Riken Shoshone, is a 1985. It still holds air great, except for a few places that have wear. I paid 1000 6 years ago, and I'd say it was well worth it.