My own research on preserving Luger grips indicates strongly against the addition of hardening oils, which include 'nut'' oils like linseed and walnut oil. For wood objects that will be subject to hard use, there is, or was, a case to be made that hardening surface treatments at the start of service life help protect. However when the objective becomes preservation, hardening oils should be avoided.
This is long but pretty good.
https://www.si.edu/mci/english/learn.../coatings.html An excerpt:
"Another instance of a traditional material being inappropriate for finish care is linseed oil or other drying oils. Oils crosslink with age, which means that they are not easily removed, and under some circumstances may darken considerably. A finish undergoing a chemical reaction which turns it very dark and makes it difficult to remove, is a problem indeed."
Also see
https://www.antiquetrader.com/furnit...th-linseed-oil
Luger grips are made of hardwood which is a very tough material. That grips can survive repeated hardening oil treatment or even more damaging substances does not mean those those substances are beneficial.