Sheath is my choice for gun oil as well and no problems to report. I store my ML with the breech plugand nipple removed and set on a clean rag muzzle down, so no worry about oil in the breech area. I do run dry patches to remove any excess oil prior to intial firing but only to prevent against a possible pressure spike - safety!

In ML's that breech removal wasn't an option I would pop a few primers before loading, just in case(plus beingI had to push muzzle to breech).