OK guys, anyone run into this one before? Initially the desc. was for the sandby (wet) compass being off more than 5deg. It was replaced, the flt deck was checked for mag fields, and de-gaused. It then went to compass rose for verification, which it passed. On check flight, it was discovered that BOTH C-12's, AND the standby were reading off simultaneously, BUT only on certain headings, and the deviation was not the same from one to the other. INS's, GPS are rock solid. The desc. is intermittent, and deviations are not on the same headings each time, it always checks good on deck.
Now the o