I wouldn't use anything that you wouldn't want getting into the aging apfelwein... Not sure how mineral oil tastes (never tried it, I only use it on my wood cutting boards, and never use those boards until several hours later)... Also not sure if having any mineral oil in the brew would produce any 'effects' such as laxative...
At the rate that water seems to evaporate through the tiny holes in an airlock, I would think that as long as you check on it every week, or three, you should be fine.
As an alternative, you could use a corny keg to age in. I would just make sure that all fermentation is completed, or filter out any remaining yeasties. You'll need to either carbonate with CO2 later, or use some yeast in the priming solution (there's online info for doing that) when you're ready...
I have an old ale that I put into a corny on Friday, with some oak chips, that I'm thinking of letting bulk age for 1-2 months once the oak comes out (used a cheese cloth bag, that I made, to hold the chips so that they'll be easy to remove). I'm not 100% sure if I'll use an airlock in the keg, or if I'll just seal it back up and let it age like that.
Actually, if you age for 9-12 months, chances are any yeast left in the brew will be beyond dormant (probably dead or so far asleep that you won't be able to carbonate with them in a decent time frame). If you seal up the corny properly, you might have a hint of carbonation when it comes time to think about drinking it.
The more I think about it, the better I like the idea of aging inside corny's...
Since you're in PA, I don't think you need to worry about the water evaporating too fast...
