These cartridges seem to wear out after two years, at most:
The handle becomes difficult to move, both left-to-right and up-and-down, with lubrication of the (obviously metal-on-plastic) shaft being unavailing.
Having devoted considerable time & attention to keeping this thing alive, there really aren’t any user-serviceable parts inside:
I think the sliding fit between the two ceramic blocks laps itself into a more perfect joint, to the extent it’s wrung together and can’t be moved. Even after filtering, our town-supplied water apperently has enough micro-fine grit for the purpose.
So I have another valve core for the collection …
On the upside, the improved spout bearing rings continue to work fine, although it’s only been five months.
The Smell of Molten Projects in the Morning 
FWIW, our Moen kitchen faucet is 3 months short of four years in service, and it hasn’t needed servicing yet.
OTOH, the American Standard two-handled faucet it replaced was tolerable. Its only problem was constant loosening of Allen screws for the valve-stem adapters; fixed by replacing the screws with ones using a better grade of steel.
On the gripping hand, the AS bathroom 2 handled faucets (about 10 years old) are fine, though the stems needed relubing as the glass-reinforced plastic wore in. Those replaced never-to-be-sufficiently-damned Delta one-handled faucets.
Three other single-handle faucets, both Moen & American Standard, of various vintages, work fine and have never needed attention. Of course, they get far less use than the kitchen faucet, so it may just be a duty cycle problem.