Canon FINE cartridges, how long do they last when refilling?

[Engine-Number9]

I'm just about done with my cheap Pixma which uses the FINE system. I printed so much with this machine.
But there's still a set of CI-541 and PG-540 FINE carts in this machine. And have been refilling this same set for over 45 times now.
Now when I print a nozzlecheck. Faint white horizontal lines appear on the magenta halftone band. Same place every time. No matter how I clean the carts or run clean-cycles.
I managed to get rid of these horizontal lines on the blue halftone a couple of weeks ago. But now it affects the magenta. And I cannot get rid of it.

How many times can I expect to refill these cartridges before the nozzles burn out. Or is there something else going on?

When I print pictures anywhere where there's light skintone color or lighter color solid background I can see very faint horizontal banding that's 2mm spaced.

 

[PeterBJ]

The cartridges are intended for single use only, so the printheads don't have the same longevity as the printheads for the separate single ink cartridges. But the printheads on the FINE cartridges must not degrade as the ink is being used up, This extra lifespan of the FINE printheads makes refill possible.

I have seen some expect to refill these cartridges 5 times before the printhead are worn out, and my results are also similar to that, so I think 45 refills is exceptional. I think you got value for your money. If the printer is still OK maybe you should buy a new set of the FINE cartridges?