probably sucking air into the oil pan. Still not sure what bolt was snapped. An oil pan bolt or the drain plug? PO had no business removing pan unless he had issue or wanted to check for T/C guide pieces. None of these bolts should have been hard to rermove. Not sure how over-torquing caused hairline crack. Should not be anywhere near that much torque...that's what gasket is for. Slow down and you will get it.
BTW, I doubt your 3V reading as you can would have quit by about 9V. keep us posted.