Kosher Liquor

The (Chicago) cRc recently sent out a reminder, in advance of Purim, about what liquors are kosher. See here for their list and note that Johnnie Walker Scotch is on their list, albeit slightly misspelled. And compare with this, that reports on a prohibition.

The Star-K does not specifically address Johnnie Walker but states as acceptable: "Scotch - All except when label states aged exclusively in sherry casks, sherry finish, port finish, or dual cask finish"

The OU says that single malt Scotch is kosher "if it was not aged in sherry casks" but you should otherwise ask your rabbi.