Crumar Musical Instruments User Group.

I recently purchased a Crumar Performer that has a keyboard issue and
was hoping someone could help me out.  All C's on the keyboard have a
very long sustain regardless of where the sustain slider is positioned
in the Strings section.  All other keys sustain normally, according to
the slider positions.  This issue happens for strings and brass.  I've
tried cleaning the contacts underneath the keyboard, swapping out the
TDA1008 chips between two sections, and the issue hasn't gone away. 
I've located the service manual for the Performer here:

http://www.synthforum.nl/forums//attachment.php?attachmentid=40221&d=1221320648

If anyone could help it would be much appreciated!!  Thanks!