Pfirst Series 2-Handle Complete Roman Tub Trim in Brushed Nickel

This faucet was installed in the half-bathroom sink by the previous owner and has worked well for nearly 10 years since we moved in. I especially like its smooth teardrop shape and brushed nickel finish. Recently, however, water has started leaking from the spout after the cold-water handle is turned off. I searched for the faucet model and believe it is 1T6-510K, but I have not been able to identify the correct cartridge model. I also tried following the installation guide but could not remove the cartridge. There is a hex-shaped metal part with a metal cylinder underneath it. I'm unsure whether both of these need to be removed. In the guide's Step 5 illustration, I see Part B (the metal ring cap), but I can't tell if this corresponds to the parts I'm seeing on my faucet or whether it must be removed to loosen the cartridge. Could you please advise on how to remove the cartridge and confirm the correct replacement part number? Does the warrenty cover the cartridge?