When I fitted my EVR not long ago I did not fit that that oring that sits in the recess on the stock slave. You don't need it when you fit the EVR.
Once I fitted the new slave all I did was fill the neck a little before I refitted the banjo and bolt.
It only took about 8 - 10 cracks of the bleeder to get good feel back in the lever and no air bubbles.

Mines been working magnificently ever since.
It's a great mod'.