Lubricant in a gearbox is primarily for the gears, You can have sealed bearings for example. I have actually designed and built (on a smaller scale) a second stage transmission which derives it's lubrication (and cooling) from the fuel. The fuel is sprayed directly onto the gears and then presurises the caseing. I don't see why this can not be modified as an emergency solution to loss of oil. All you would need to do is fit a fuel nozzel to the gearbox casing and attach a solonoid and fuel line to a boost pump. When the pressure drops and the temp starts to rise, you activate the solenoid and spray fuel straight on to the gears untill you find somewhere safe to land.
I'll get my coat...
