The find of the century, the holy grail, do you know how honoured you are Nickw to be the keeper of such a treasure?
You and the record will certainly go down in record collecting history.
If it were me I wouldn't sell it for a while just to etch myself in the history of what I had descovered, I would have as many photos of myself and the record taken as possible and have them framed and mounted. I would then when I decided to sell it on, make sure that the deal included that I were documented as the finder of the record to go down in any future reference books etc.
It is a sad fact that when you do sell it, if you do, you will feel a great loss not to be the holder of it anymore and there will be an empty space where it once was that is never likely to be filled, but hey! you'll be a rich man.
Very well done, I am very jealous, but in a good way and I am very pleased for you that you have found this up til now elusive gem.