I have an old (WWII vintage)but very trustworthy Ka-bar Mk2 that is a user, not collector material, but still in very good solid condition. Problem is, the leather in the handle is probably shrinking just a bit with age, and the crossguard is getting just a little loose. Is there a way to treat the handle and "plump-up" the old leather to tighten things up without ruining it? Oil, silicone, wax, just plain water, etc.? Any help appreciated.