The sandwich style filter has the return line plumbed back into the filter via a banjo.
This recirculates air that cannot be easily bled off.
When the TDI engines came out this problem got corrected.
It is almost impossible to get all the air trapped out of the system.
I recommend installing a sedimenter close to the tank, then a 12V fuel pump that comes on when the ignition is switched on.
This will expose any leaks as any area that was previously leaking will drip fuel.
Next get rid of the sandwich filter and install a TDI style spin-on or replace the banjo bolt on the return line with a solid bolt so the return line fuel actually goes back to the tank and not back into the sandwich filter.
With the 12V pump, you'll have a self bleeding system and you'll never have issues bleeding your fuel system again.
PM if you need a source for sedimenters and filters.
They are relatively inexpensive.
Uncle "Richard" Douglas has a Land Rover with big wheels that never gets stuck... until he breaks something so it won't go. Uncle Douglas always breaks something. - Anna Crowther at the Conclave 2012 (AKA Carburetor Neck)