Supposedly the only thing Kodak ever would recommend touching a neg would be a Kodak Photo Chamois. It is a animal hide that you keep wet in a jar, then squeeze the water from it and clean off the film, that has prev been washed. These Kodak chamois cloths are no longer made (of course). However they pop up on the bay and here ever so often.

This is how their instructions read. I had a trashed neg that came clean following the below.

Here is what they look like (note this is a sold one):