I've repaired and cleaned a few cardboard revolver boxes over the years, both S&W and Colt. Mostly cosmetic repairs (gluing and re-squaring box corners, removing oil stains inside the box with cornstarch powder, gluing worn paper edges, etc.), and removing old Scotch tape. The lighter fluid does work great on removing tape and residue. The only time I will use steam on a cardboard box is to reshape the top/bottom/sides if they are bent or bowed- lightly apply steam through a cloth, then apply flat pressure, and allow to cool. I don't paint (touch up) worn areas of the box, I prefer the box to look its age- but it's been repaired structurally. After repairs/cleaning, I always apply a couple of coats of Renaissance Wax to the exterior of the box. Here's one similar to yours that was repaired. Good luck!