I am a somewhat experienced scanner/restorer of slides, but I was given a really bad case recently. The 50s Kodachrome appears to have had some kind of acid spilled on it. The emulsion (but not the film itself) is eaten through in spots, and there is a central "bleached" area. The worst part is that there is a tan translucent stain across the eyes of the subject. I am willing to work on this slide as much as it needs, but the tan area across the eyes (behind glasses) makes the subject (my grandmother) look like a racoon, and I'm not sure I can mend this with image processing.
I tried PEC 12 and apart from taking the old orange varnish off, did nothing. 90% Isopropyl alcohol also did nothing. Thanks for any advice!
I restore old photos occasionally, and I've found the instant-fix/healing tools work well for some cases, but most damage requires doing it the hard way at some point. If you have a scanned JPEG sample, and I could fix some part of it in an hour or less, I'd be willing to give it a try.