That yard looks so meticulous that it's easy to assume it's not grease related, but many a pretty Genny hides accumulated neglect under the hood. I have seen one grill in that shape that the owner blamed on squirrels chewing the hose to the regulator.
This is true. I just had to swap out the hose on my latest rehab because some mice, chipmunks, squirells whatever had chewed on it. It didn't leak as far as I know, but I could see white reinforcing threads where they had chewed. Better safe than sorry.
The damn mice or whatever like to chew on the control knobs as well.