fell off the its end of travel. The suction valve would not open when using the sander and the area was like a dust bomb. It reminded me of old shop. The valve is working against gravity because the whole assembly is not level due to clearance issues (may or may not be the issue here).
Anyway, I slipped the gate back on its pinion and verified operation. Cleaned the area. The new sanding station is so nice and works great at keeping the dust down. When something is not right it becomes very obvious.