Wild, I went to change the o-rings and add the missing shims to my diff last night, my diff only had a light coating of oil left on everything inside.
But I played around with shims and o-rings, noticed the stock o-rings are quite hard, and fairly thin, without the shims I'm guessing they never had any seating pressure at all, hence so much leakage.
With the shims, using a .1mm there is still some play (maybe still a shade too much), but with a .2mm it feels a touch tight, I did see some build guide elsewhere with a guy sanding and shimming for that perfect no play to no bind ratio.
So I'm just going to try the listed .1mm shim, but I will also try a Mugen o-ring, the Mugen o-ring is actually a little thicker and a bit softer, it's also a little tighter on the outdrive shaft, not by much.
So far since building it, it's not really leaking, but I'm surprised there is still a tiny hint of weeping after sitting overnight.