SR4 serial numbers

[Northern Tim]

Hi folks,
I'm looking at buying an SR4 but trying to work out the age of it. I've done numerous seraches of google and the forums here, but struggling to work it out, mainly because the serial number on this boat seems to be a different format. Any ideas?
AVB15770M81A-A

[chewy]

Its usually the last two numbers, ie yours would be 81.
Downhilldai is the lad to speak to on all things SR.

[Downhilldai]

I'd say 1981 too.