I only have Amaro Averna, do not why it was... oily? the texture was thick. I went exactly for the Lime Bitters, but it was equilibrated, so use some real lime. It was better, less bitter. So why bother? is interesting, a twist in the Last Word, contributing but not definitive yet. Its ok, not perfect, but fine.
100% agree on it being too cloying. I was considering switching to a London Dry on the 2nd attempt, but I might try your adjustment. I'm not sure if the Montenegro really stands a chance up against the strong Chartreuse and Maraschino flavors.