Looking for some advice. I have a special commemorative decanter celebrating 50 years of manufacturing at Hill Street site of Diageo. The whisky is a rare blend known as Jonnie Walker 1820. It comes in a presentation box, and has a covering letter proving its authenticity. It was only given to employees, and was never **** to the public. Can anyone give me an estimated value, and an idea of where would be the best place to sell. Thanks.