Helicoil would be best but if you used a self tapping bolt for a car or truck oil pan, it's probably too big now for a helicoil.
You really can't use o-rings unless a groove is built in for them, they tend to squeeze out the edge and it's a fine line between tight enough and too much.
Get a copper washer that will crush a bit and seal.
Next time you tap any threads with a self tapping bolt or helicoil tap, put grease all over the tap to catch 80% of the aluminum, then do a flush and filter change and your good.
Ease up on the aluminum, too many guys strip drain plugs; I just did one yesterday AM a few hours before a 250F flat track event when I got begged for help. Needless to say - HE OWES ME!!
All our government does is distract us while they steal from us, misspend our tax $ and ruin our country