Yes thats correct. But ouch on the price! lemme see if the place I bought still has any.
Yup. That's exactly what all those companies are doing. That link happens to be all drum, but they sell the same one as disk/drum by removing that little valve and giving them a different part number. Its cheaper for them and it works fine. I used one for 25 years. Just got to keep an eye on the fluid level.