I recently got my grandpa's hat, it's a nice hat except for the mystery gunk on it. It's hard and has some residue running from one side that suggests it may be some type of aged adhesive, I'm thinking either it came with some embellishments or he glued some feathers or something on at some point. It could also be where something got stuck to it in storage. It's been shoved in a basement for many years without any protection.
I also need general cleaning and reshaping advice, it was partially crushed by a bag of old clothes, and had some rodent droppings on it.
This is the first "real" hat (meaning made of a high quality leather and with true craftsmanship) I've had and I'm not sure how I'm supposed to care for it other than occasional leather conditioner and waterproofing.