Welcome to the forum.
These are great inflatables, but don't under-estimate the work involved, especially if seams have gone. These boats are over 35 years now, and if it's gone in one place, you can be assured it's likely elsewhere.
Polymarine is a good site for instructions for PVC repairs. It's likely to have the nickel plated inflation valves. The Zodiac Delrin diaphragms and cap seals will probably be required for an airtight seal and are available.
If you're handy - then repairs are possible. Low humidity is essential, with the right 2-part glue and an area that's dust-free with stable temperature. Degrease solvent, masking tape, seam roller, brush, sand-paper. Take your time, preparation is everything.
Areas to look at in particular are the cone ends (rubber deteriorates), speed inflation tubes, keel tube (goes at the crease) and of course transom (separates).
You'll need to get the boat to operating pressure to see that it's holding air, once you've repaired the bow seam.
Keel tube is 220Mbar and main tubes 240-280Mbar