Part of the issue with the black tank valve is the geometry of the cable as it enters the gate. The valve manufacturer, Valterra, shows on their schematic a minimum of a 6in. straight approach to the frame. Ours (and I suspect all) does not have that. I sprayed silicone lube into the gate (don’t know how much actually got the the gate mating surfaces) and manually worked the gate up and down with the exposed cable at the gate and that seemed to do the trick. Previously the gate did not fully seat - about 1/4 inch shy. I think as others have pointed out, the lubricating the entire cable length is the way to go. There is a lot of skin friction on that length of cable especially with all the loop d loops it does.