It possibly may have been Transmission fluid. I appreciate the the tips and will try the mineral oil. Here's some pictures of a Cheetah XX with different swing guard. Looks to me like a repair/replacement to me but don't know for sure. I still like it never the less.
Your welcome. Yes, that swing guard has been replaced. Case used the same swing guards in XX as they did decades prior and to present day from the knives i have seen. You seemed to have a pretty nice roll of 11-1/2s in one of your pics. I assume this swinguard is the only one-off. I have XX to 81' 11-1/2s and Cheetah and all have the same swing guard.
On the mineral oil, I suggest that you go to the General Knife Discussion forum and put "mineral oil" in the search box for that forum. You will get varying opinions on the use. It appears most agree that useful when used sparingly. Some used a "bath" on stag to rehydrate it. I personally would be concerned about darkening the stag by doing so but if the stag is dry and brittle, I might try it. A mineral oil bath could be detrimental and overkill on a bone knife and could possibly damage it by removing the color. Just what I read, never done the bath treatment. As I said, I normally just apply a light coating on the knife then wrap the knife in a sealed mason jar overnight in a mineral oil lightly soaked chamois cloth.
Not sure there is any remedy for the possible tranny fluid treatment. I guess the owner thought it was a good idea at the time. Still pretty knives just real dark.
Since I am real intrigued by the 70' Proto and 71' Production Cheetahs, both low runs for a 1970s knife in my opinion, just how many are still around. Just my curiousity make me wonder how many are left since some may have been lost, broken, misused, etc since possibly the owners did not realize what they had nor possibly cared.
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