There were split washers for the wall mountings, though I can't see them helping there much, for example because I simply do not have enough exposed remaining bolt to accommodate the washers!
The bolt that came undone was elsewhere, holding the vertical to the horizontal bar that carries the rotors and bounces up and down a fair bit in strong gusts.
I'm going to have to keep my eye on all the bolts for a while!
Rgds
Damon