That waste pad on the left is almost entirely full of crud. You need to piezo-flush it directly and order a replacement from CompassMicro as well.
<edit out> damper comment, I see you replaced yours </>
Wells is sending you something re: damper shortly. Check email.
If it was cart-related, you would see back-pressure zooping up the line from the print-head after a clean. Sharpie your cart levels before you do either an init-fill or maint-clean and then you can see the carts that perform well and those that don't.
/// EDIT> Re magenta cart. Can you send us a photo of it vs the other ones you have? Also, like Dana said, don't use it. We are working on debugging some x800 related issues. support at inkjetmall dot com