riff_raff, I remember doing a US Army accident course in '71 and mention was made of an engine oil leak in the Chinook which travelled up the gearbox drive tunnel and acted as a blow torch on the gearbox, with the same results as your photo. How do you go about predicting an event such as that? An unenviable job attempting to dot all the i's and cross all the t's of what can occur.
small oil jet orifice becoming obstructed by walnut shell debris trapped inside the gearbox housing oil galleries from grit blast cleaning during an overhaul, the overhaul procedures were modified and the design of oil jets were revised. It is now standard industry gearbox design practice to include a "last chance" filter screen on every lube oil jet to prevent debris from obstructing the small diameter metering orifice holes
Everything old becomes new again, in a way. The P-47 in WWII European theatre were having an inordinate number of engine failures. Cause was sand from the casting process not being successfully cleaned out.