My friend (the one who had all the Remington M1903s) used mineral spirits on one of the stocks on my recommendation and it turned out blotchy and terrible - which was about as terrible as I felt for making the suggestion!
Although I am not a proponent of not cleaning off cosmolene, some are, and since you mentioned you might want to sell the rifle, probably best not to clean it.
"We make men without chests and expect from them virtue and enterprise. We laugh at honor and are shocked to find traitors in our midst."
--C.S. Lewis