In the 12+ years I have sold printers, small holes in dampers has been the most common problem with ink delivery. I don't know how the holes are generated - I used the term 'pinhole' loosely - but they do occur. Maybe it is poor quality injection molding, poor quality plastic raw material and small breaks in the ink line where it connect to the damper. Some dampers have an O ring that seals the assembly. I have seen splits in the O ring that have been the source of air bleed but I don't know if all Epson dampers/selectors have the O ring component.
With the older models: The seals of the damper connectors are the most likely place to let air in or with enough ink pressure ink out (seldom). The membrane (most likely PET) thermo/ultrasonic welded on the polyethylene damper house could have a leak at the weld, cleaning them with a syringe had that risk of pulling them apart there. Older dampers showed less flexibility in the membrane and the small stainless steel spring inside could in theory puncture the membrane in time. The membrane is there to equalise ink pressure on feeding and demand and adapt the ink pressure to the atmospheric pressure, at least on the the older Epsons including some pressurised models. It could be that it changed in newer models and another ink pressure control is used.
It wouldn't surprise me if the new damper model includes a sensor that actuates a valve in the ink line when the ink pressure/feed near the head drops, the opened valve to fill the ink buffer again. Something like that existed on the 10000 model but there internally in the head assembly.
With OEM carts the risk to get filth in the lines in negligible but pigment settling (say coagulation) in the ink can build up a barrier on the damper's sieve in time or with infrequent printer use. Inks have improved though.
Air in the head shows when the bad nozzles change in quantity and place. Frequent cleanings may not help at all, sometimes a night's rest does more. Thermal heads suffer less of air as the nozzle channel is less complicated and the thermal pump can still function with some air enclosed, piëzo pumps need fluid to create the pumping action, any air there will just act as an air spring and the ink isn't pumped.
met vriendelijke groeten, Ernst