As one commentator said, its odd that the attorney-client privilege is broken only when the attorney is sued for Legal malpracitce. However, it is less than clear how the ‘at use” principal plays into legal malpractice litigation.
Here is a case where the defendant attorney wants information from the successor or suing attorney which will help the defendant on a staute of limitations argument [loss of faith in the defendant might start the statute running]. In this Ohio case defendant attorney was not permitted the communications. Details.