I'm on my third hood. This time they added a lower sheet metal shroud below the original one. .... and a new hood. Both of my headlamps were blown out which may support the idea that it's a place where hear collects. Prior to this replacement there was a heavy coating of carbon collected under the hood and along the vent path. The inside of the tail pipe was not coated, so the theory was that it was from the melting black grill. The new hood has a larger opening and shows no sign of melting (after about 10 hours) but I noticed a light coating of soot. My guess is that this deposit is from exhaust gas, that still passes under the hood. FYI... no apparent oil consumption increase and all intake vents appear clean. I do run the machine at full RPM and plan to reduce that by a notch or two to see if this changes things.
Bouvier
Bouvier