Parts pricing in the States has evolved over the forty years I have been in the business (both Retail and in OEM environments). In Clark's prime back in the 1970's they used to use Point-Part Numbers to throw off the new After Market parts suppliers springing up. It also allowed them to use different pricing depending on the Client. In the late 1980's and early 1990's Crown used to make a big deal that they still printed a list price book for the End Users. If the local Dealer would not sell the part for the listed price in the book the factory would sell it to them direct. This campaign was targeting Raymond Clients since Raymond did not publish list prices and often charged over list.

There was a time when Dealers could & would regularly make 10-15% margins on trucks but unfortunately those times are gone with OEM's raising prices and Customers unwilling to take the increases especially and on large deals, Dealers often are only making 2-3 %.

This has forced Dealers to make margin elsewhere and the focus on the parts that lead to above list mark ups. Labor rates are also inflated along with higher first time travel charges. All necessary to stay in business these days.
Did I mention that Crown no longer offers a Published List Price book to anyone who asks but I believe the still can supply it to only a select few clients.
OEM's can make 40-125% margin on parts (but remember they must stock more to support the country's demands) Dealers 30-45% margin plus their markup of any where from 10-35% typically.