I've been having problems with my KCS 55A HSI. At engine start Saturday morning, the heading indicator aligned properly in slave mode, but by the time I taxied to the run-up area and made a left 90 deg. turn, it settled off by about 70 deg. I put it in free mode and realigned it using the toggle switch, but when I taxied onto the runway, it was out of alignment again. About 10 minutes into the flight, I put the indicator back in slave mode, and it aligned and worked flawlessly for the rest of the flight, and for the subsequent two legs that day. This behavior has occurred 3 times now over the last 2-3 weeks, and it's only after engine start on the first leg of the day. The KG102A is an overhauled unit that was installed 4 years ago. I'm spoiled by the large display that the KI525A provides - it's the only indicator I've used for instrument flying - , so I'm not inclined to opt for a digital HSI replacement until something of similar size is available. Any thoughts on whether it's the gyro again or another of the components would be appreciated.