differential fluid

Hello, Apologies in advance if this is the incorrect forum for this post. I’ve been reading through several posts and I‘ve narrowed down my answer but I’ve never changed the differential fluid on my Jeep so I’m kind of scared of messing it up even it seems simple enough. Based on the info...

Just replaced my diff fluid for the first time on my 2018 JL Sport S (at 92,000 miles- yeah, I know). Everything went as expected, except for this piece I found on the drain plug of my rear diff. It doesn't look like a gear tooth - it's got a groove in it, leading me to believe (hope?) a...