As a starting reference point, your printer is 13 years old. You obviously lucked out, getting one that has held up and served you well for such a long time. That can't last forever. Even the very best specimens of the very best products eventually wear out. Any time, effort, or money you put into servicing your printer is going toward one that is way past its design life and living on borrowed time.
The manufacturer also doesn't support it forever. At some point, it isn't cost effective to manufacture and stock replacement parts, or even ancient ink cartridge models. That's basically contrary to the business model. To make money, they need to sell you a new printer that takes new ink cartridges.
With good sales, you can find a replacement printer with better specs in the $50 range. It comes with starter ink cartridges and a warranty, and doesn't currently need service.
Given that, not many people would put money into servicing a 13 year old printer, so there's not much demand for the parts and support that the manufacturer doesn't want to provide.
With that in mind, some models are serviceable by users. The pad is accessible and you can clean it or replace it. If you choose to clean or replace it, you have a good chance of getting ink stains on your clothes, your skin, every surface that isn't covered in plastic, anything close to where you move or discard the cleaning solution, etc. If you're not meticulous in your prep and execution, you may spend more replacing stained stuff than the cost of a replacement printer. But yes, you can do it if it's designed to be user serviceable.
Other models require serious printer disassemble and potentially replacement parts that Canon sells only to authorized service people if they still manufacture them. Your question states that your manual puts your printer in this category.
You might be able to do it yourself if you're technically inclined, a little inventive, and have the right tools, especially if you can lay your hands on the service manual so you don't destroy your printer in the process. If you are in this situation, see the previous advice about spending more to replace stained stuff than the cost of a replacement printer.
So say you go the technician route. If you don't have a local service center, you will need to properly prepare, package, insure, and ship the printer (likely shipping costs both ways). Getting it to and from the service center will cost you a significant fraction of the cost of a replacement printer before anybody even touches it.
What if you have a local service center and can avoid those shipping costs? They have an expensive technician to pay, overhead, the job of disassembling and reassembling the printer, potentially replacement parts, and a messy job that has a good chance of getting ink stains on their technician's clothes, skin, tools, surfaces, etc.
Even if they can get the parts, there are risks working on a 13 year old printer. if it breaks in their care, they're responsible for it. If they fix it and return it, and the 13 year old printer finally gives up the ghost shortly after the customer gets it back, the technician obviously broke it and they have an irate customer. They really don't want the job, and they have negative incentive to make the repair cost attractive. Guess how the service cost will compare to purchasing a replacement printer?
So yes, you may be able to service the ink absorber yourself, but don't. Start shopping for a new printer. But that's just my opinion. For perspective, I'm an engineer with a lot of design, build, and repair experience, who once had a printer with a full ink absorber and zero common sense.