Intermittent Loss of Oil Pressure @600rpm

Unknown

With knocks gone, and engine running,  been chasing down a random loss of oil pressure within about a minute of startup.




At start pressure rises to 4psi holds pretty steady, then drops quickly to zero, like the screened area of the sump went dry.  Shut down and restart, still no pressure.


Priming the pickup extension tube side of the pump with fresh oil will return the oil pressure but only for 30 seconds or so.


Found the brass soldered on fitting on the pickup extension tube outside the sump was cracked and the tube would not hold a vacuum. Other than that I could find no other reason for the loss of oil pressure. Pump springs good, ball valves clean, pump does pump correctly.


Is this cracked brass fitting unique, both my copper tubes have these brass fittings, two are cracked. 


Can a copper tube be used after flaring its end?


Thanks


Jack