I've only skim read this thread so sorry if I've missed anything.
If a dealer had fitted something to my van and it had been done so poorly that it had fallen off and although didn't, it could have caused an accident and injury, and then they brushed off any responsibility when informed about it, then I would feel it my duty to make sure other potential victims were made aware.
Ask yourself how you would feel if in six months the same happens to another and it does cause an accident?
The dealer seems to have made it clear they don't want to know. They have had there chance to respond.
I would out them then forget about it.
If a dealer had fitted something to my van and it had been done so poorly that it had fallen off and although didn't, it could have caused an accident and injury, and then they brushed off any responsibility when informed about it, then I would feel it my duty to make sure other potential victims were made aware.
Ask yourself how you would feel if in six months the same happens to another and it does cause an accident?
The dealer seems to have made it clear they don't want to know. They have had there chance to respond.
I would out them then forget about it.