We offer free tech support via this support forum, and do our best to respond as quick as possible (though, we don't promise "instant" response). Our office hours are M-F 9am-5pm, and you responded to my last message after I left on Friday evening, and I have been working on several priority things things this morning, so haven't had a chance to respond sooner.
If the missing nozzles were causing the banding, you would have banding thru out the image in any area that uses this ink, not just at the top and bottom of the sheet. Can you attach a photo or scan showing an example of your problem for me to see? This will help me better understand what you're dealing with. A scan/photo of a printed nozzle check would also be helpful to see.
You should always print with the best quality settings for optimal results.
Are the other five channels printing well?
Generally, if the missing nozzles move around, that's often caused by air. I could send you a new magenta capsule to try, to rule out the current capsule causing flow issues with this channel, but since you had the same results with this channel using a different cart, I suspect it may be a physical issue with your printer, unrelated to the carts or inks you're using. I also see you purchased a print head cleaning kit in your initial order with the first set of refillable carts (without ink). What ink did you use in the first set of carts? Did you get the print head cleaning kit because you were having issues at that time?
Print heads don't last forever, and the 1400/1430 printers are not professional quality (though can produce very nice results, especially considering their low cost). There is a lot you can do to get the best results and longest life from your printer, but some things are out of your control (we've received a 1400 that didn't work right out of the box), and many people use the 1400/1430 as a decent quality low cost printer, that they replace every year or so because they generally don't last as long as professional model printers.
Having said all this, I would be happy to review printed examples of your output to see if it sheds new light that would help me help you get back to printing.
Best regards~ Dana