I would try assempling, then dunk in vine for a few minutes, rinse, then give it a quick bakind soda bath.
After that allow it to dry enough to form well and do your wet forming and allow to dry completely after this.
Then do your oil/conditioning.
The only thing Ive used on vinegaroon is leather balm with attom wax and it stays nice and black. As stated though the process brings tallows or waxes to the surface of the leather which makes it about as sealed as its gonna get IMO.