I've never had a bad HP 18 but that sounds like too long in a sherry cask which tends to give that sulphur, rubber smell.
My favorite malt for a long time was Bowmore Darkest Sherry Casked but my last bottle was awful, again probably overdone sherry but other weird notes of awful perfume. I should have returned that bottle but didn't so now it is mainly used as a BBQ sauce component, for which it is surprisingly good! Along with some House of Parliament Sauce, Bowmore Darkest makes a wonderful rib marinade now that we are in BBQ season! If I were you, I'd try to return it if possible before resorting to cooking uses for an expensive dram.
That bottling made me shy of all Morrison Bowmores as I've heard other people have had the same problem, even with some non sherry bottlings so I don't know if yours and my cases are bad bottling techniques, bad casks, 'corked' bottles or what (corked wine I know but not corked whisky). If I try another Bowmore I will return it right away if it is not good.