Mineral oil might be better. Over a long period of time (6 months to a few years) vegetable oil (cooking oil) will slowly oxidize, changing its color and creating significant odor and possibly hard deposits on surfaces. Generally mineral oil will not do that. Mineral oils (e.g., Nujol brand) are less well known, but easy to get in places like drugstores.
Thanks for the info Paperdoc,
I had thought of cooking oil as LePhuron suggested but I also work in the food industry and know what damage cooking oils can do to electronic components over time.
But thanks for all the info.