On a twin cam if they are leaking, base or head there is something wrong. A few examples, the heads were not torqued accurately, one or more of the surfaces were not straight and true, the studs are pulling, the orings on the dowels at the base are doubled up (oh my is this a bad one), proper lubrication of the bolts, and more.
People assume their torque wrenches are accurate. They are not always and even comparing a click stop to a digital will surprise you the stated allowables, + 4% VS +1.5%, if memory serves me right. So when is the last time your torque wrench was calibrated? If it was is the tool of high enough quality to stay put for a while? Personally I have several torque wrenches and use different tools according to the application. I torque heads and torque plates with a CDI digital that was calibrated at the factory last month.