Just a thought? Why are reduction gearboxes viewed with a little scepticism in the aviation environment, whereas automotive applications rarely experience failures? I would have thought most high mileage vehicle operators have recon lumps fitted long before the gear box goes U/S? Although the argument for auto engines not producing 75% power for long periods and not really being suited to these applications seems to be a valid stand point.
The problem with "car engines" in aviation is in the design. Short stroke car engines designed to deliver short bursts of high power low torque performance is diametrically opposed long stroke high torque (relatively per cc) low power aviation engines.
I would guess that gas turbines will feature in t5he future, just got to get those costs down!
PG.