Every 46AX I've handled in the last couple of months.........

When they've got a good needle setting that is rich enough that they're not running too hot, their exhaust oil will show up on the airplane clear. If I've set the needle too lean, they've shown black oil on the airplane.

I would make the judgement from oil on the airplane after a flight. What the oil that's been left in the muffler looks like wouldn't mean a thing to me.