Hi,
I have also beefed up the sloppy airbrake mounting with two triangle of epoxy plate drilled 8mm to fit the central tube. I then made a U shoe in e/plate and dropped it over the top of the tube and glued everthing up solid. Ligth modification and no slop at all.
All I have to do now is fumble with getting the two cap heads tight to fix the control arm in position. Patience is the virue sometimes but it will be done.