An OVERSIZE OIL DRAIN PLUG, a taptered, self-tapping plug of the same pitch, but slightly larger diameter than the original plug, offers the possibility for a permanent and inexpensive solution to your problem.
Ideally, M12 X 1.5 oversize, but another pitch may work (as some have reported).
Costs less than $ 5; if it DOESN'T work, you're no worse off than when you started (less a dollars for the plug).
The slight additional diameter provides purchase for the threads, with enough fastening force to seal the hole with the typical washer.
Now, I await contrary posts, from forum members who run, screaming, from the room, at the mere thought of an oversize oil drain plug!
As mentioned above, the oil drain plug is NOT a fastener of high mechanical stress; its only function is sealing the crankcase at atmospheric pressure. My motto: "If it seals, it heals!" I've had miracle cures with oversize oil drain plugs; you might enjoy the same--inexpensive, permanent, durable fixes.
For those who claim oversize oil drain plugs do not work, please explain why oversize oil drain plug factories are working multiple shifts, producing these products!