nipple

I'm going through the process of replacing all the fluids on a new-to-me 2004 with 30k miles, and I need some help fixing the rear brake. The rear brake was mushy (but functional I think) when I bought it. Here's what I've tried: - I went to bleed with the basic method seen in this video...

I bled the rear brake a little while last month and recently found it has little as a little leak...I unscrewed the nipple and tried to seat it properly and screwed it in again but can't eliminate that little drop come out from the other side on the nipple screw.. May be I need to re-seat it...