Thank you both for the information.
I tracked down the manufacturer using one of those websites, and called them this morning. The current owners bought the company after my boat was built, and told me that there are several types of materials used on those earlier boats.
She thinks it's a canvas cover over vinyl bladders - and told me that a standard vinyl pool liner repair kit would work to repair any leaks. They do not have any new bladders left, but they do have new (old stock) covers - in case I wanted to replace mine. Trouble is that the cover costs nearly as much as I paid for the boat.
(They are willing to bargain since the demand for these covers is not so high.)
She did mention that I may not want to pull off this cover - and just "leave well enough alone" since the bladders are holding air - which doesn't inspire much confidence, honestly.
There are several options, including a Hypalon retro-fit tube that they have. Before going that far, I'd still like to paint or coat the canvas cover to brighten it up and perhaps extend it's life (and my confidence).
Any advice on what I could use to do this? I have read that Hypalon paint is a suitable coating for "canvas rafts" - and may be just what I need to help maintain the boat.
Anyone with canvas experience? Any advice. Thank you all - this is a great resource.