I would be tempted to leave it as you will probably find it is the cold and damp that is causing the problem. In the summer it will probably lift again with the heat. I had the same problem with the roof lining in my old Vitesse. It used to amaze me how it would drop in the Winter but go back to its tight self in the Summer. I would imagine in time that this may get worse ( once it starts and then repeated change in temperature therafter each year)however but I would perhaps leave it until the Summer to see if it does go backas you dont want to make it worse by trying to make it better
