Advice on Vintage Day-Date required.

[N.J.L.]

I need your advice on this vintage Day-Date I was offered today.
This Day-Date has plexiglass and I like the cream dial, however I am unsure about the BEX 251001 case number at (6 o'clock).
I have taken a couple of poor photos on my Blackberry.
The asking price is £2600 and I have conducted business with the seller for over 20 years. The watch is sold with no paperwork or history and has recently had a service.
The watch is not quick set therefore I asume it pre dates 1983. Any information would be appreciated.
Thanks in advance.