When you say "seems to sail much better on port tack" how are you determining that? Speed? Apparent wind angle? Can you quantify it with some numbers?
One thing to keep in mind is that on Bene, Hunter etc with inmast furling, the sail does not come out of the center of the mast. It comes out an inch or two to starboard. I'm sure there is some aerodynamic affect that provides better air flow on one tack. You do mention the mast seems to be stragiht. Is it plumb? There is a difference. From side to side do the shrouds seem to be tensioned equally? Does your boat lean to one side or the other naturally? Are the jib cars set exactly the same?