I had good luck with a crack/hole by packing the hole with salt grains (dry), applying a moist "salt patch" (damp paper towel bit that was dampened with brine) to the hole, and then continuing to dry it for 2-3 more days at higher humidity (about 85%- created by turning an upside down colander over the drying board and storing the whole thing in a hall closet w/ door shut). Every morning and evening when I flipped the cheese, I'd make sure the patch was still damp, and occasionally (maybe once a day or less) take a butter knife and smooth down the hole/crack to encourage the surfaces to knit.