After some time, the reaction time of buttons can be reduced, not through wear and tear, but through dirt and gunk. How many of us can say 100% we always have clean hands when mashing it out on the fightstick? If cared for properly, you should have in the millions of button presses during the life of your buttons, but you may occasionally need to replace the microswitch (for example https://www.focusattack.com/sanwa-sw-68-button-micro-switch/ for Sanwa), but even then, you may have sluggish or stuck button presses. To clean up your buttons I would advise the following:
1. CAREFULLY remove the button from the top-plate. These side clips molded in the buttons are very frail at times. If you are afraid they will break and are working from a panel where you can just remove the plunger while keeping the rest of the assembly in place, go that route. You will need a small flat head screw driver.
1a. Insert the screwdriver into the small holes on the sides of the rim and lift the plunger tabs up carefully. You may have to repeat on both sides and massage the plunger out from the top at the same time.
2. Using a gunk cleaner (DO NOT SATURATE) and a microfiber cloth, scrub all the inside of the button (rim) and the top and sides of the plunger.
3. Using a silicone based cleaner (like Brillianize https://www.focusattack.com/brillianize-instant-detailer-pack-for-plexiglass/) use a microfiber cloth (DO NOT SATURATE) to polish the same areas.
OPTIONAL: Popping out and cleaning or replacing the microswitches on all of these models are the same: squeeze the sides of the microswitches from below and pull lightly. From there you can clean or pop out and replace.
This maintenance, if done properly, will maintain the life of your buttons for many more presses to come.