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If it is leaking from the cap, and you didn't break anything, and your sure your o-ring is good. Then I am almost certain your cap o-ring is upside down. I made that mistake and had the same problem. Make sure the beveled end points down. Try that and let me know.
I guess by the design of the stock fuel regulator, it would also act as a check valve. Like Tenn01PSD350 said, if you are not returning your fuel, then you are not regulating either and it is going to be hard not to have a leak. With no regulator and no return, the leak is not going to be your only problem.