A few darknet markets were exposed using this method some time ago (as well as other IP leaks, such as email headers). It is the type of leak that gets picked

A few darknet markets were exposed using this method some time ago (as well as other IP leaks, such as email headers). It is the type of leak that gets picked up by curious researchers within hours/days of a market launching - not something that would linger for months and be left for the FBI.