PIXMA G2020 won't print blue, although window says it is 2/3 full

[kiddee]

My Canon Pixma G6000, bought 7/19/23, is not printing blue.  I have done several print head cleanings and a couple deep cleanings.  Ink windows look like they are all 2/3 full, although I have never had to change or refill the inks, which is rather amazing. Suggestions? 

[Stephen]

Some units have a replaceable "maintenance cartridge," which is where the sponge lives. Others don't. Most home-use printers don't have them because, in regular use, people don't tend to fill up that sponge, but businesses tend to print more, so they may need to replace it.