AP1 owners: please replace your valve retainers and keepers (aka cotters) with AP2 or aftermarket retainers and keepers!
Valve retainer/cotter/springs on AP1 engines are known to fail, whether or not driven hard. The issue lies in over-revving of the engine, e.g. mis-shifting or constantly hitting or exceeding the rev-limiter (over 9000RPM). When the engine is running over 9000RPM, the valves float and a result the valve springs close at full force. The keepers and valve are the only things stopping the retainers, and with such force the retainers crack or split. So with AP1's that see the race track, there is higher potential to crack the valve retainers since VTEC only happens when RPM's are higher. On the date of this post, AP1's are now 2 decades old. Most AP1's would have seen multiple owners, so it's difficult to know if the valve retainers are still healthy unless you crack open the valve cover and do the inspection yourself.
We replaced the valve retainers in this with AP2 valve retainers as the owner wanted peace of mind after purchasing the car secondhand. It's still not a good idea to over-rev the engine, but with the AP2 valve retainers inside it prevents the sudden need for a new motor.