I have an old Simrad Roberton autopilot with a linear drive controlled by a J3000x course computer and an AP11 head unit.  The Linear drive, course computer and compass are all fine, but the head units (I have a spare) suffer from the usual problem of switches that don't always work.  I have cleaned them with pure lab grade alcohol with little improvement.  I remember being told that some other head units are a direct swap and ask if anyone can tell me which ones.

I am not actually such a new member, having posted here before, but failed miserably to log in and had to join again!