I go straight to the nuclear option. I burn baby burn!!! I just got back from two weeks in Cozumel with a group of a dozen divers. Half of them were complaining about mask fogging to different degrees. They tried toothpaste, salt, baking soda.
So I gathered all the offending basks and subjected them to my 7/11 butane lighter technique. I burn the inside. If there is ANY black...that means oil...that means fog. I wipe the black with a damp paper towel and I burn again.
One mask I had to do that at least a dozen times until no more black when burned. Even some masks that had 50 or more dives on them were coming up pretty black on the first few burns.
Caution.....you don;t need to hold the flame on the mask for a long time. Just a second in a spot. Remove the oil a little at a time. Don't try to burn it all off at one time. My Coz boat name is now The Heater!!!