I have always applied the policy of replacement before failure. 1HZ Landcruiser get a recommended timing belt kit every 100,000km so I do waterpump, all belts, hoses, thermostat at the same time. I even keep a spare rebuilt injector pump in my spares cache 🙂. I even have brand new in boxes H55 transmission and matching transfer case too, amongst brake pads, linings., bearing kits and even a complete fan to flywheel 1HZ engine with 200k on it, 2F petrol motor 125k I bought 30 years ago. The list goes on……
Now collecting aircraft spares 🙂