So I was looking at the rear of my IRS and determining how to fill it. As i was doing this I saw this "feature", yellow arrow pointing at it. Its machined, polished and I can't really tell if it needs a plug, or if something I haven't gotten to yet, goes in there... I have a complete MkIV roadster, delivered 1/20/23, with 2018 3.55 Complete IRS Diff, delivered from FFR as part of my kit. Any help is appreciated...