Yes, the buttons are definitely limited in lifespan (due to material).
You can clearly tell just by visual inspection which ones were used most... and are about to break. Not a tragedy, though, because even broken they usually are still operational.
(and there are replacements)
Similar is the pad sensor sheet glued to the bottom frame. It
will wear out.
I didn‘t check sensor response when I got my 4K (didn‘t know about that screen), the machine looked nice and not heavily used... but the sensors were almost deaf.
Replacement of the sensor sheet isn‘t too difficult, but you have to disassemble the top half of the machine and placement of the sheet needs care.
Any remaining glue of the old sheet must be removed, and the new one sticks like hell, no adjustment possible after placement.
The display ribbon can also wear out, if the machine has been opened frequently.
Mine obviously was exactly that... and by fiddling with the ribbon I managed to fry a part of the display circuit. Learning by destroying
The ribbon is either expensive or difficult to find... so in case there‘s damage it‘s worth „restoring“. That‘s not an official procedure, but manageable. Some patience applies.
Essentially you snip off the worn section and then (very carefully) remove the isolating film on top of the dark lines. These lines are conductive ink and easily wipe off.
Hidden gems: on my board a transistor was fried (and „repaired“ in a bizarre way), but still works. The respective smd transistor is a rare part with internal bias resistor.
(the transistor is related to the display)
I peeked this only when I disassembled the whole machine to find the cause for non-working digital connections.
Nothing suspicious found - but digital connections came back to life. Dunno if this was by replugging all connections or the use of AkaiSys
There was 1 happy accident though: the 4K was sold with 256MB of Ram, but actually contained 512MB. Reseating the Ram did the trick.