I wonder if the diagonal has a hair line crack in it and venus as a bright enough point of light will show it up , the moon on the other hand is distended across the field so this streak would be invisible ?? ( hidden by the image ) , I seen this in my only bad OZ post chapter , a 2 inch diagonal from Andrews arrived with a crack across the mirror , nearly invisible to the eye but bright stars and Jupiter knew it was
there .
ps. Andrews replaced it without even asking for the cracked one to be returned , awesome costumer service .
Just a thought .
Brian.