The old wraps were made of cellulose acetate, and are always shrinking. It's worse when the drum is exposed to temperature extremes. One day ALL vintage wraps from older drums will be cracked, since the shrinkage never ends.
I've seen some amazing repairs using epoxies, fillers, super glue, etc. The cracks can be filled in, wet sanded over, and then buffed out. Some people add a coat of clear lacquer for more protection.
There's not much you can do with a heat gun. If you do use one, be careful as the wrap is very flammable. The whole thing can go up in flames in an instant!
Thanks,
Bill