When you click on links to various merchants on this site and make a purchase, this can result in this site earning a commission. Affiliate programs and affiliations include, but are not limited to, the eBay Partner Network.
Yes it is all part of the pan and the pan is a casting with the threads and the sealing surface (the part that the aluminum sealing ring mates against) are machined. You need a smooth surface for the aluminum sealing ring to butt against. And of course both are machined together for both to be "true" to each other.
I am very surprised your pan had no oil residue (or did it) due to no aluminum sealing washer being installed there. I know after I install my drain plug with a new aluminum sealing washer and it is torqued to spec (37 lbf.ft.), I might have the odd oil drip hanging off the drain plug after a few days...and that is with an aluminum sealing washer. I just loosen it and re-torque it and that takes care of it.
Yeah, no drops of oil at all, even without the washer. But with probably 90-100 ft-lbs of torque maybe it's not so surprising?!
I was worn out (mentally) after getting that drain plug out but will finish the job this evening after work. Hopefully now with proper crush washer, new drain plug, and correct torque it will continue to be leak-free.
Looking at that pic, it appears that who ever worked on it (Dealer, Indy or DIYer) never inserted the 8 mm hex bit more than half-way. Its not a press fit and the bit slides right in. Problem is, it might be sliding back out when the person is about to apply some torque to it...in the correct direction...I hope.
And maybe some are not using a torque wrench (you really do not have to if you have the "feel") and due to paranoia, are over-tightening the drain plug out of fear of it loosening.
I just slipped an 8 mm hex bit into the same one pictured above marked SKS and it can be inserted 8 mm (5/16").
This is the original drain plug in my 2015 after at least 8 oil changes over the years. You can see where the hex contacted the corners. Sorry, I should have taken that pic at an angle to get a better view of the sides.
UPDATE: OK I was wrong! There WAS a crush washer in there previously. While getting the stuck drain plug out, I must have accidentally lost it in the waste oil pan somehow. But while cleaning everything up I found it at the bottom of the pan. (My oil catch pan doesn't have a strainer or anything on it.)
Anyway, everything is back together, oil filled to the correct level and last thing I need to do is reset the oil service indicator. I borrowed a PIWIS 3 from a friend so hopefully using that won't be too complicated.