Hard to tell what the problem is. Why did you replace the QD inlet? By two parts, do you mean the internal adjustable orifice that screws into that QD fitting? The whole unit could need cleaning or adjusting or parts replacement or all 3. The Schrader valve gets corroded easily, the orifice or soft puck seat could be damaged or out of adjustment, or the purge valve could need adjustment.
I've got several of these, they have been the octo/inflator setup for both of my BCs for many years. I find they need frequent cleaning, probably because simple soaking doesn't get the job done. Don't store it anywhere hot or near solvent fumes, like in a closed cabinet or garage. Oceanic used crap material in their purge covers for many years and these are prone to becoming brittle. I always carry the allen wrench and other tools necessary to adjust the orifice and purge valve, since mid-service interval tune-ups are sometimes needed.
The service manual can be found online, and you can get through servicing and adjustment by following it. Or pay someone else to do it. If you're sure of the status of the internals, start with the orifice and purge valve adjustments to see if there's any improvement.