"one more mention, the left tank(good one) does not have a vent to say from the header, just the right tank has the vent to the header."
if both wing cap vents are working properly ,..it should not matter if there is only one vent from the header to one tank,..not both ,..it almost sounds like a vacuum is being established somewhere that it over taking the vent in the right tank ..since the vent goes from the header to the right then to the left thru the transfer line,..is there a check valve anywhere in the system?
Chase