Unless there is a catastrophic failure of a shock, we are not able to “check the shocks” as a regular maintenance activity because general wear and tear does not show that much physically. While it is true that there are some seals where gas or oil can leak slowly, it doesn’t ordinarily cause a drip that you can see clearly. That is why we determine the time to replace these items by mileage rather than visual inspection when on the rack.
I had a friend who had over 200,000 miles on his truck, and I told him, “Buddy, you need to replace the shocks on this vehicle.” I had been attempting to convince him to change the shocks since he passed 100,000 miles on his odometer.
Note: If a shock has been on the car over 60,000 miles, then that is the time when the Automotive Safety Administration recommends changing the shocks and struts. Buddy had been going through tires on his truck, but finally allowed me to change the shocks and struts.