I only use mineral spirits if I am prepared to re-oil or refinish the stock. Alcohol, as mentioned, will remove shellac or French polish finishes, and both mineral spirits and alcohol will seep under even the most careful masking.
A lot of the guys on the Parker site swear by Murphy's Oil Soap for gently cleaning and freshening old stocks that are not going to be refinished. Available at any hardware store. The Parker boys have posted some before/after pics of the Murphy's treatment, and the results look very nice. I think they usually oil or wax the stock after cleaning.
