Hi Jim. Sounds like a nice boat. Avon have an excellent reputation for quality - your boat has many years left in it. There are 1970s Avon's still in regular use. Have you got a photo?
The tube material is hypalon. So you need a hypalon repair kit which will comprise of spare hypalon fabric to use as a patch, and 2-part hypalon specific glue. There's lots of repair kits on Amazon/ebay etc along with specialist retailers. In the US, West Marine sell all the stuff you need. There's lots of posts on here about how to do repairs.
Here's a good example of what you need. The tool is a seam roller - you might need to buy that separately on Amazon etc - Home depot also sell them.
PS. Yes, the last two digits of the HIN are the year, so yours is a 1991.