Brake Fluid Service
It is recommend to have a yearly flushing and bleeding brake of your brake system with .4 brake fluid on 2006 to present Harley Davidson Motorcycles.
One of the properties of .4 brake fluid is to absorb moisture. The fluid absorbs moisture then becomes corrosive. That is why the paint is peeling on the top of your master cylinder.
.5 Brake fluid is for pre 2006 Harley Davidson motorcycles. The brake fluid breaks down due to the heating and cooling of the brake fluid, temperatures can be in excess of 200 0degrees. Although it’s not corrosive it does collect sediment that collects in the bottom of your master cylinder and calipers which is abrasive and that will give you poor brake feel.