Ah, what the heck. Made it this time with Old Forester, Dolin Génépy and Campari, and it still works fabulously! Made a double and it was just as good as it warmed up in the glass.
Great suggestion. Yes Benedictine's always good in everything I've tried it with. Have you tried Boomsma Claerkampster Cloosterbitter? It's a stand up substitute for the Chartreuse if you can get it.