I, too, had problems with the greasy kids' stuff until I switched to the type of modeling clay sold in art supply stores (don't recall the specific brand). I don't know what's in silly putty, but I'd be very careful to avoid anything that contains silicone. It is real hard to remove, and it plays heck with adhesives and finishes, as it prevents them from adhering.
Paul
Good point Paul. I have not encountered any problems after using Silly Putty, but one should avoid silicones on guns if at all possible. I will try to find out what is in Silly Putty before using it again.
John