I have had this mostly under control for 25 years. There is no cure, only management. My Grandfather had it too so I didn't have to experiment. He already knew how to keep it under control. He used tar soap.
Use only tar shampoo or soap to wash with.I recommend once a day. Denorex tar works well. Be careful, there's two different kinds of Denorex. One has a red top and contains salicylic acid like Head and Shoulders.
You want the blue top one. Tar promotes the shedding of a layer of skin and is very effective at removing excess oil. This will help keep pores clear to prevent the secondary infections.
Keep hair very short. Essential to keeping scalp clean.