The FAR29 MRGB 30 minute requirement is for a loss of lube system functionality condition, and does not necessarily imply that the MRGB is operating entirely without lubricant. And as for the S-92 MRGB being qualified as having a lube system failure event considered "extremely remote", that went out the window with
AD 2009-07-53
That single point lube system filter failure should never have gotten past a proper FMEA of the S-92 lube system.
I have designed some rotorcraft MRGB's. And there are several established ways to ensure a 30 minute loss of lube capability in a rotorcraft MRGB. The most common approach is to use high temperature gear (X-53) or bearing (M50NiL) materials for the critical gears/bearings, that can operate at temperatures up to 600degF without losing temper. The other approach is to provide a secondary, "total loss" back-up lube system that provides just enough lubricant flow to keep the friction heat generated by the critical MRGB gears and bearings within their capabilities.
MRGB lube systems are now always designed with the lube oil pipes as integral parts of the housing castings, in order to minimize leaks. And potential oil system leaks are one of the main things that the FAA looks at when certifying a new MRGB design.
Also, personally I would never have used titanium fasteners on a maintenance item, like Sikorsky did on their S-92 MRGB oil filter housing, due to the known inherent nature of titanium fasteners to gall and seize if not installed under perfect conditions.
Regards,
riff_raff