Fuel may not necessarily escape when air enters.
An 'o' ring seal, located in the fuel filter's center, can serve as the ingress point. I was able to diagnose that using PTFE tape.
It is true that a fuel pump can release air. Repair kits have been utilised on that. Engine that was much older, though.
A leak off kit was rigged for the 646. Some tubing and plastic soda bottles from a dollar store made up the bulk of it. Clear and efficient.