Quantity of Parts Sales to Third-party Customers

I am interested in knowing what percentage of a dealers parts sales are to outside companies? For example independent body shops, after-market repair facilities, distributors, gas stations, quick oil-change facilities, etc.
In addition, does anyone know a statistic that states what the average dealers parts sales are per year (all areas of the business...internal, over-the-counter, etc.).
In addition, does anyone know a statistic that states what the average dealers parts sales are per year (all areas of the business...internal, over-the-counter, etc.).