Vintage Old Spice soap is known to break down chemically over time and can be quite harmful. I will PM you my address. Ship it to me and I will test it for you.
Definitely use it. Although, it could spoil you on soaps forever. It's one of the best ever.
I'm gonna try it out this weekend I have used vintage Colgate and Williams before but never O.S. I do use my grandfather's old Old Spice mug everyday just with modern soaps. This will be my first time to use one with the original contents.