If you do anything at all, just wipe it down. Unless the finish is totaly gone I wouldn't touch it. And if it is gone, there is a certain way to refinish the stock without ruining the rifle's value. Do you realize what you have there? Check this site, after that you may not want to touch anything on your rifle. Go down to the collector's forum, Mosin Nagant Headqurters and see what you can find.
Also check here: