[plymjack]

Well done here - a really good post.

As to how long - well it depends on so many factors that it is hard to say. The methodology used now is call Reliability Centred Maintenance (RCM) and attempts to calculate the replacement times of components based on failure. So if you know it is failing after x then you replace at x-10%.

So with brake fluid it is generally around 5 years for the worst case so they suggest 3 years as a safe time. If you change it yourself then every 3-4 years would seem fine too.

With filters it is much more condition related (dusty, hot or city driving?) so is more likely to be an inspection based (say every 6-9 months) and change based on that. Obviously once you have done one you can predict the cycle more accurately.

If someone was to run a reporting service for such items it would soon become a useful resource for everyone??