I don't advise opening the LEC's equipment, but you could in theory connect a laptop to the smart jack card and check the error log there.

I've had to prove 'intermittent' problems that way before.

Most CLECs will not believe it could possibly be anything wrong in their network unless they can either {not loop the smart jack} or {see the red light on the SJ} and they can be gosh darn stubborn about it too.