Mel, do you think that's a function of nuts being properly torqued and working loose, while the torque seal fails to break, or of builders/mechanics making a procedural error and applying torque seal to fasteners they have not personally verified to have the torque set properly?
In my opinion, these situations would be cases of torque seal being applied when the fasteners had not been properly torqued.
Torque seal is a valuable tool when it is
used correctly. It needs to be applied as each fastener, hose end, etc., is torqued.
We use it extensively in our RV-12iS production division. At final post production inspection, if torque seal is missing from any torqued connection or fastener, it gets squawked and has to be checked for proper torque with a torque wrench and then torque seal applied before the airplane is signed off. I did quite a few post production final inspections prior to switching to DAR duties (when acting as DAR I can't have any involvement with an aircraft prior to the point of doing the certification inspection), and I would occasionally find torque seal missing but I believe in all cases the connection was fully torqued but torque seal had not been applied.
In my opinion, this is the only purpose of torque seal.... as a visual indicator that something was at some point torqued properly.
It is a great cross check for any home builder, but should be an absolute requirement on any build where multiple people are participating.
It was standard practice for every connection with the TeenFlight build program that I lead, as well as the One Week Wonder build project done during OSH2018.
As Mel has pointed out, for it to have any value it requires proper discipline when being used.
What torque seal should not be relied upon for is as an indicator that a fastener or connection is still at a proper torque value once the airplane is in service. Once that is true, about all it shows you is whether the assembly has been taken apart at any time since the torque seal was applied and even then that is not total proof. I have seen connections with improperly applied torque seal, taken apart and then reassembled with it being very difficult to tell that the torque seal has been disturbed