Gentleman.

I have the chance to purchase an old B.S.A. Meteor .22 air rifle. The rifle itself is in good working order but is missing the rear sight and one forend screw. It looks like the old style Meteor but lacks the fluting on the stock. Serial number N4623. It has been well used but shoots well.
It is fitted with one of those old B.S.A. plastic (yuk) telescopic sights. The sight is in good nic, complete and working. When I was a lad in London these sights I seem to remember sold for 42 shillings. It has that horrible moving reticule. Being cheap and plastic can I assume that their life span was limited and that good ones are not very common now?
I bought one back then and it put me off telescopic sights for a long time. Mine only survived a few field trips. No one can argue that this is a practical bit of kit.
I’d like to know that if I buy this rifle what would be my chances of getting an original rear sight. I assume it was metal?
How old is this rifle?
Is it worth buying for the scope alone? As a collectors item?
Any guidance would be much appreciated.

Barry (New Zealand).