Originally Posted by
FBinNY
The problem isn't that the part will loosen over time. It's that it's difficult to maintain adjustment while mounting and centering the brake. Once you've done that you're good to go. Meanwhile you can keep looking around for the part and might eventually find one off a crashed brake.
Exactly.
If the missing part is anything like the corresponding piece on the secondary pivot, it was poorly designed. That piece is an aluminum nut (6mm) with a steel set screw. They seem to crack at the set screw fairly easily (I've seen at least three do this). I have a drill press and a machinist's vise so I may just drill a stainless nut if I have to wait too long.