Sox6, thanks - I am reasonably familiar with CS/FAR 29.
This is the clause that allows exemption from demonstrating the 30 minute capability:
Unless such failures are extremely remote, it must be shown by test that any failure which results in loss of lubricant in any normal use lubrication system will not prevent continued safe operation, although not necessarily without damage, at a torque and rotational speed prescribed by the applicant for continued flight, for at least 30 minutes after perception by the flight crew of the lubrication system failure or loss of lubricant.