The ambiguous information (according to some in this thread) currently available, which could probably aid and assist Captains in their judgement and final decision making, is perhaps due in part to the ambiguos wording in the Regulations.
The questions should go back to the OEM and the Regulatory Authority -
1) under exactly what loss of MGB lubricant conditions will this a/c ensure 30 minutes of continued flight
2) what failure modes causing loss of lubricant, other than external cooler/line failure have been considered
answer to 1) will probably answer 2)