I've seen and heard of mosins having cosmoline removed from the stocks by taking the stocks of, wrapping them in paper towel or something and putting them in a couple of black trash bags for a few days and leaving the stock (trashbags and all) in the dash of a car for a few days when it is hot and sunny to melt out the cosmoline.
I personally have not tried it yet, but whenever I manage to get another mosin (after I foolishly sold mine) I am going to try cleaning the stock up the same way.
I'd say that if it is cosmo on your mauser it might work, and I don't think that it has even a possibility of harming the gun (my opinion)