OK, as suspected, the Glenmorangie company does not offer valuations. For this you'll need to contact McTears.com or Bonhams.com. They feel, as many do, that the perceived value of any collectable item is effectively determined by how much a potential customer might desire the item, and how much he or she is willing to offer when it appears on the market.
The last Christmas bottling at Leith was bottled in 1995 and one bottle was made available to each company employee. My contact at Glenmorangie will pass along your request to their marketing department in case they have an interest in the bottle for their archives. If this is this is the case, they'll let me know and I will contact you. Give them a about a week.