I've recently bought an old, full length HW77. I've never had one of these before so, when this came up at a good price, well, it was rude not to

It's showing it's age a little - some marks in the bluing and, it looks like someone tried to win the ashes tour with the stock.

At some point in it's life it's had the SFS treatment - it's very smooth to cock and shoot - I was hitting 10mm kill zones on a knock down at 25yrds with ease when I went to look at it.
A quick chat with SFS yesterday revealed that it's more than likely had a stage 2 tune (whatever that involves).

It's missing the front and rear open sights - not a problem for now because I can put a little Hawke on there but, I would like to have them on there eventually.

The safety isn't working at all - hopefully an easy fix with bits from my spares box.

My question for the knowledgeable folk on here is, is there a way to find out the month and year of manufacture?

The rifle is stamped 'Made in W. Germany'.

The serial number is 1031829.

I found a search thing online last night - this said it was most likely manufactured in 1986.
I was just hoping to be more specific if possible.

All help and replies appreciated