The top Allen screw was missing and the bottom was fitted with a rogue hex bolt which was too short, hence the gap.
There was no O ring on the back of the box either!
So I will get these items ordered and treat the box to another bush whilst I'm at it.
Edited By C J on 10/03/2018 23:39:19
Edited By C J on 10/03/2018 23:41:40