I just finished a COMPLETE tear-down of a '67 rs/ss. Used products called AeroKroil, and SiliKroil that I heard about on TNN's "Trucks" about a year ago. I only had one brake line bolt I couldn't get loose.
Rarely had to even let the product sit overnight. I don't think I'll ever use WD 40 again.
Not avalible in stores, see www.kanolabs.com
I've got no interest in the company,just was a great product!!! Dave