As a followup to my original post on this topic, I double checked the
artificial horizon while on the ground, and it appears to be showing a
slight left bank when the wings are apparently level.  That would
explain why, in IMC, with the artificial horizon level, the plane
turns slightly right.  Sometimes it's the simple things, really!

This was the result of a quick check on the last flight...I'm going to
pay a lot more attention on the next flight.

Keith