[DutchmenSport]

As I remember from the days when I was 15 years old working in my uncles gas station / garage for a $1 an hour pumping gas and learning some stuff about auto mechanics, the only time drum brakes need to be turned is when they wear and end up with grooves because the shoe pads wore down and metal was rubbing against metal. If there are no grooves or worn uneven then clean up the oil and grease as you have done and the drums are fine.

If the breaks are still not working well, then it's possible they are not getting enough electric voltage to activate them correctly (which actually happened and was the root cause of my failure on a previous travel trailer, the wires were too thin carrying the DC electricity). Or, the pads are simply worn down and not making good contact when the brakes are applied.