RV-12 with D180 and AP74 gets lost when I dial in heading 180. AP works fine when turning to headings from 220 cw around to140. West, North, East are solid, but the southern cone, especially 180 is a +/- 10 degree search never finding the set heading. Have tried adjusting roll settings on the ground and in flight, but doesn't help. Sensitivity of 7 seems to work well with the other cardinal headings. Could this be a shear pin issue?