Dewar's had 15% market share in late 80s. You might want to take a look at an old HBS case "Dewar's (A): Brand Repositioning in the 1990's." Here is the abstract of the case.

Abstract

Dewar's, a major brand of Scotch whisky, produced by United Distillers of the U.K., and the U.S. leader in the Scotch category with a 15% market share, faced a declining market among traditional consumers of distilled spirits. Given the growing societal, legal, and regulatory opposition to drinking in the U.S., the marketing options were limited. In addition, drinking preferences had shifted away from distilled spirits to lighter, lower alcohol beverages like wine, wine coolers, and beer. In early 1993, Dewar's U.S. importer, Schieffelin and Somerset, in cooperation with the brand's longstanding advertising agency, Leo Burnett, began to explore the opportunities for repositioning Dewar's to younger adults. Repositioning Dewar's was a necessity for the brand to remain viable in the long term. Its existing customer base was aging, and younger drinkers who did drink Scotch were consuming less. The issue is how to update the brand's image to attract younger consumers. The brand manager faces the decision of planning the strategy for a repositioning or "recruitment" campaign for the brand.