So your helmet is gunky and smells.
It takes hours to clean and yet the smell comes back.
Next time you clean it use a anti-bacterial treatment like Polygiene. Then use a Buff® to keep it that way. A Buff® is anti-bacterial for life and kills germs. The source of the smell.
Are your side cushions also worn out from your beard? A Buff® will prevent that.
The image shows a Original Buff® used as helmet liner / face mask combination. The design is called Cashmere Blue and is an evergreen in the collection.