About fifteen years ago, I bought a second-hand Reunion leather gig-bag from a mate of mine. The bag was in excellent condition, but had obviously been used/stored in numerous smokey pubs, etc.
Two days opened up and left outside in sunshine and a light spring breeze, did the trick as if by magic. Try a couple of decent days towards the end of February if we get them. You'll be amazed. Good luck and don't bin that bag. 🤥