As far as I know it's the same for most boats, with Avon's it the last three numbers that are important. e.g.
Serial number ending in 605 = June 2005
Serial number ending in 195 = Jan 1995
With regards to repairs, I'm sure you can find the problem and hopefully solve it yourself. Have you checked to see if the valves are leaking?
Also post some pictures if you can as we always like to see a new purchase