Sorry to have no magic answer, but just wanted to add my 'jingles' for you and your lovely border collie (horse people send 'jingles' for good thoughts/luck/hope to those in need...jingles referring to the jingly curb chain that some bits have).
With any luck your detective work will pay off
, and in the meantime you know that there are folks out here who care about you and your furbuddy. Do keep us posted...you never know (last year one of our dogs came down with a rare condition, and we were lucky enough to have someone identify it even before our excellent vet).