Decanting is the single best habit in this hobby and it took me years to adopt because it looks fussy.
The moment that converted me: a bottle I had used for four years developed mould, and it had happened because I filled a pen that had been sitting inked for months. One contaminated fill, one dead bottle of something discontinued.
Small vials cost very little. Fill several at once from a fresh bottle, close the main one, and put it away. The main bottle then effectively never gets opened again.