looks like a vacuum issue at the cap as a first guess. the pattern is similar to what is caused by air gettting into the cap and not sealing. also that pattern can be, but rarely, the manifold screen filter has clogged. this manifold filter might be the case on your printer becauce a bad cap top seal would result in a failure to both black lines in that the vacuum to them is universal. to better get a seal at the cap, clean off the cap top and also just swap cap tops with a different head (they pull right off) to see if the issue changes. as for air leaking... an air leak will result in ever decreasing positive ink pressure at the head. which will cause black ink starvation further into a print or ink falling back toward the cart.
there are some way to isolate the issue so that you are stabbing at issues, and if fixed, not accidentally.
first off diagnose if it is an air leak at that damper, or a vacuum situation at that cap. swap the two black lines/dampers (cross the lines to the black head) and see if the issue moves to the new head. if the issue stays at the left side of the head, nothing is wrong with your printer from the dampers back. if the issue moves to the right side of the head, than you have a bad damper, air leak, or clogged ink line. similarly you may be getting inadequate vacuum from that pump (no likely because the other side of the head is fine). in this case to diagnose, swap pump tubes to that head to see if the issue changes.
