get a new copper washer of your bolt size, drain oil into a clean container, use a file to smooth the sump surface where the bolt flange sits.
install bolt with new copper washer - tighten to recommended torque, loosen, tighten loosen and tighten again - It wont leak.
For future use - buy 2 of such washers so you always have one ready to use - dont throw away the old one - they are reusable forever - just heat them with a welding torch and allow to cool down - done-ready