In order to set volume and mute state for a clip with Dual Mono audio a ges_clip_find_all_track_elements is needed.  Dual Mono files produces two audio track elements.

Something like the code below would work, but there's probably a more efficient way, since most of code is taken from ges_clip_find_track_element.

GList *
ges_clip_find_all_track_elements (GESClip * clip, GESTrack * track, GType type)
{
  GList *tmp;
  GESTrackElement *otmp;
  GESTrackElement *foundElement;
  GList *ret = NULL;

  g_return_val_if_fail (GES_IS_CLIP (clip), NULL);
  g_return_val_if_fail (!(track == NULL && type == G_TYPE_NONE), NULL);

  for (tmp = GES_CONTAINER_CHILDREN (clip); tmp; tmp = g_list_next (tmp)) {
    otmp = (GESTrackElement *) tmp->data;

    if ((type != G_TYPE_NONE) && !G_TYPE_CHECK_INSTANCE_TYPE (tmp->data, type))
      continue;

    if ((track == NULL) || (ges_track_element_get_track (otmp) == track)) {
      foundElement = GES_TRACK_ELEMENT (tmp->data);
      gst_object_ref (foundElement);
	  ret =  g_list_append(ret,foundElement);
    }
	
  }

  return ret;
}