Hi Greg...welcome to Pentax Forums! There are commercially available negative cleaning solutions that are supposed to work well as well as solutions that can help with scratches. I have read several posts on this site regarding such, but have no personal experience in use. I am aware of one product that comes highly recommended. That is PEC-12 Archival Photographic Emulsion Cleaner. It is used in conjunction with PEC pads. You can buy it at Adorama:
Photographic Solutions PEC-12 Emulsion Cleaner, 4 oz PEC
and many other places. A quick search will bring up multiple links.
Steve