They all list the disc/drum master cly but none have the check valve. I went in today and was talking to the store manager and she was clueless. Up walked up one of the employees that was a friend of mine from way back. He is an engine builder delux. I ask him if he knew the difference between a drum master and a disc master and he started to explain the residual valve to the manager. She was dumbfounded. I ended up ordering two and see how they come in. I bet they won’t have one.