As long as your bottle has been stored properly - out of sunlight, in a cupboard or liquor cabinet, in cool temperatures and has avoided extremes of temperatures - it should be just fine. Also, it should have been stored in an upright position as to avoid contact with the cork.
Regarding the value of the whisky, something you need to keep in mind is that once it has been bottled, the whisky stops maturing. Therefore, even though it was bottled at 8 years, many years later, you still have an 8 year old whisky.
You may want to contact Chivas Brothers Ltd through Pernod Ricard for more info:
12, place des Etats-Unis
75783 Paris Cedex-16
+33 (0) 1 41 00 41 00
I'm not too sure how lucky you will be getting in touch with someone, so as a back-up, you can always try to contact the Edradour Distillery and perhaps they can direct you to someone who can steer you in the right direction. The only blended whisky The Edradour Distillery in Pitlochrie produces is The House of Lords. Here's a link with contact phone numbers and a contact form. http://www.edradour.co.uk/placeframe.html
Once you get to this page, click on "Visit the Distillery".
Best of luck!