I don’t think you can save them, except maybe if you did some aggressive scraping to try to dislodge the foreign bit that have embedded themselves into the leather. The cost of replacement cowhide strops is only a few dollars and the value of the correct embedded media is too low to matter.
I’ve tried several types of strop media beyond what WE offers. I’ve made them out of maple, cedar, aluminum and brass. Each seemed to work at some level, but were still subject to cross contamination. The one nice thing is that I could remove the platens, flip them and remount them with a fresh face to start over. Can’t do that very well with cowhide. Or, in the case of the aluminum and brass, use them as substrates for DLF. It is interesting that diamond particles seem quite happy to embed themselves in just about any media. I haven’t used them for at least five years. Maybe I ought to resurrect them. I did like the brass, but didn’t use them much before I switched them over to DLF duty, so I don’t really know if they worked more like a strop or more like DLF.
I just remembered another advantage of the metal platens – if you thought they were contaminated, you could re-lap them on a piece of sandpaper.