I have an issue with my STEC-30 AP on which I was hoping someone might have some insight. Issue: Works fine in NAV, GPSS, and steer mode. Follows the GPS magenta in lo and high threshold modes appropriately. On HDG mode, however, about 6 months ago, it began flying 10 degrees to the LEFT of the heading bug, regardless of the direction of flight. I recently tested this on NW and return SE legs in low wind/turbulence conditions and it was 10 degrees off for both legs. DG is Sigma-Tek. History: 2 years ago I had the DG overhauled by mid-continent and reinstalled. I had just purchased the plane at that time and the DG was already failing and the HDG function didn't work at all with the AP. After overhaul of the DG and a service of the AP, all functions worked (although on the initial flight on all modes there was a very small oscillation/correction of the ailerons which went away on the next flight and has not returned). Over a year later, this HDG issue arose. I asked the avionics person who installed the DG whether it could just be a calibration issue with the heading bug spinner. Paraphrasing (I don't remember his exact words), he said that the DG has no easily accessible calibration and that the problem was the DG, not the AP. He didn't seem like he wanted to deal with it. Since I had the DG overhauled only 100 hours ago, I am not excited about the prospect of removing the DG and facing unknown trouble shooting and/or overhaul costs just for the hassle of having to point the heading bug 10 degrees to the right of my intended heading. But, it is annoying. If someone has dealt with this exact issue and knows if it is easily repairable/corrected (and who they know that can fix it), please let me know.