I always used the leader in the sheath and the overhand knot as you mentioned. I looked online too and it looks like the leader won't go in the micro.
Appears they just take out the lead and tie it like braid.
https://tuf-line.com/superline-info/https://www.lakeontariounited.com/fishi ... -leadcore/I found that the regular lead core was real slippery and the overhand knot could move. I always use a drop of crazy glue. Seemed to fix the problem.
I just use the cheap stuff from the dollar store. I think it's four tubes for a dollar or so. Don't mind throwing them away when they glue shut.