They then stick out of the front of the printer also making ink levels easy to monitor...... Note not recommending that ebay seller it was just one of the first results i came across. Also be sure to buy the right carts for the model of Brother printer.
Also keep in mind that there is a problem with most refillable made in china carts for brother , epson etc printers where they use spring as seal for ink outlet.
The problem is that springs supposed to be stainless to prevent rusting, now the china guys just use some cheap springs that are zinc plated that rust and make havoc to you printer. The solution for brother is to use large XXL carts that stick out from the printer and to modify them. The modification is to remove the spring. Since that carts are refiled plugged into the printer the seal in not needed.
When you want to remove the carts you can plug the both holes ink in air to avoid any leaks. Stainless springs are anti magnetic, test them with magnet (somewhat impossible until you remove them from cart)
Ive not heard of that issue, i wonder how the spring rusts? The spring near the ink outlet which is part of a valve AFAIK, ink does not even even comes into contact with, so in theory it should take years before that spring started to rust even if it was cheap tin.
Even if ink does make contact with it surely a better solution rather than just removing it for ink to potentially go everywhere would be to replace the spring with the springs from your original brother carts???
You need to test the springs with magnet, stainless metal is anti magnetic.
Replacing the springs is possible but the plastic ring that holds the seal ring needs to be welded like in the factory, I could not find same sheet plastic, so I used different polyethylene plastic.
If one plugs both holes (with provided plug) of the cart before removing it, no ink will leak out until you remove plug. So obviously you must plug temporarily the outlet hole before removing the plug from fill hole.