STEC30/GPSS offset to the right of course

[Guitarmaster]

I have an STEC 30/GPSS that likes to hang out to the right of course.  It does this on both GPS and VOR/LOC.  In addition, it tracks about 4 degrees to the right of the heading bug.

I have checked the pot under the bottom, right mounting screw and it is trimmed all the way CCW.  In other words, it should be tracking left of course with this setting.  

Here's where it gets weird....

On the 430W, if I set the CDI to auto then back to .3, it centers up with the GPS, but Still tracks to the right on a LOC.

This feels like an installation error, but where would that error be?

Thanks!

[DMM]

If the plane is in trim and flys hands off, I would try cleaning and re-seating the electrical connectors.  I read somewhere that  the left/right course and HDG  deviations provide a voltage differential.  A dirty connector can bias the voltage. 
Take all this with a grain of salt - I'm no expert.  Just telling you what I would try.