Vista, thanks for all your help with this.
For anyone reading this thread looking to upgrade to a Hurst short shifter please note:
May, 2014 Hurst started manufacturing breather slots into these shifter to alleviate this problem. I have just got off the phone with a hurst rep who had to get in contact with engineering to confirm they did fix this.
Going forward if you purchase any new Hurst Short shift Manual Shifter, Billet Plus - HurstShifters
there will be no need to mess around with a breather/pressure release as they have fixed this at factory.
Woot woot, placing my order tonight.