O' Reallys POS

If you haven't already yanked the MC off try this. I had the exact same problem last summer with mine and I tried all of the same things but check this too. Make sure that the top itself is going all the way down and compressing the gasket when the retainer is locked. The top on mine was formed so tight that it couldn't seal no matter how much force I applied with the retainer. I went all around the outer edge of the cap where it bends down over the reservoir and slightly reshaped it so it would allow it to go all the way down onto the reservoir and squeeze the gasket. I've had no leaks since. Good luck!