All fixed.
Very poor design. The problem was these thread inserts that were in the lower bracket, they have pulled out. All 4 of them.
Don’t know why it’s designed like that, the whole they were in is an 8mm hole. The hole on the L bracket is only 6mm. (Why not simply make them both 8mm ?).
Anyway, found a hardware shop and bought some tools and some M6 nuts bolts and penny washers. Used the wife’s lip balm to stick the lower washer under the bracket and then put the bolt through, with nice large washers above as well. So all sorted and rock solid.
These are the silly thread inserts.
View attachment 294736
Washers on top. Using M6 bolts.
View attachment 294737
But and washer below. Zero movement in the brackets now.
View attachment 294738