I called Peter at GDL and found him to be very informative. After reviewing the symptoms he also felt that the problem was most likely the amp and added that it was probably not worthwhile to do anything with the actuator at this time.

Although not likely, I'll try the to check the brake light circuit to ensure that this is not the culprit. If this proves OK then I'll probably have GDL rebuild the CC amp.

Thanks all,
Paul