Usually look at doing mine when I begin to get a misfire, on the F's I've found its the rota arm and dizzy cap which needs changing regularly plugs and leads tends to last pretty well.

 

This! - unless its broken, don't bother trying to fix it.

However, if you are determined to spend some money, then you are correct with the recommended mileage interval.

 

Oh, I am not looking to spend additional money, I'll wait until there is an obvious problem with the leads before replacing them, thanks.

 

Ya I usually wait until I have an issue with misfiring. The HT leads sitting on the hot engine get soft over time and spark onto the metal rocker cover. If you let the car run in the dark you will see the leakage sparks onto the rocker cover, then your loosing spark from your plugs. If this happens it time to get new leads.
Hope this helps.
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