The cosmoline should come off the stock fairly easily. Some guys actually put their stock in the top of a dishwasher and let 'er rip. It's supposed to do a great job. The oven or the sun will work, but expect the stock to ooze for a while, it may take several cleanings to get it really clean.
If ye love wealth better than liberty, the tranquility of servitude better than the animating contest of freedom, go home from us in peace. We ask not your counsels or arms. Crouch down and lick the hands which feed you. May your chains set lightly upon you, and may posterity forget that ye were our countrymen. ― Samuel Adams