Old greasy undercoating?

I have what looks like old greasy undercoating on the underside of my Duster. It’s not hard to the touch but like old grease.
I am wanting to clean it all off and undercoat myself since it’s 49 years old. I don’t have a rotisserie but have the body on blocks so I can get under it. Anyone know what will eat or dissolve this greasy mess?