In the service book it may state that short journeys are classed as severe use and therefore need a shorter (5000? 6000?) service interval.

To my knowledge they have no way of proving you've not done 30 trips of 100 miles though.

I've never heard of a rusty camshaft being caused by this though, and a few cars in our family have had the shopping trolley treatment.

Most warranties have an upper mileage limit, but never heard of one with a lower mileage limit!!

If it's under warranty and it's failed then it should be fixed.

Ask the dealer to show you which warranty clauses you have broken. None I'll bet.

Short journies = condensation (especially in the cam cavity) = [usually] sludging
But rust? sounds dubious to me.

Edited by Cyd{P} on 22/05/2013 at 08:39

Cam position sensors usually rely on a magnet and a steel pin in the cam. As the cam rotates, the sensor either detects the magnet passing by, or the pin causes the magnetic field to fluctuate which is detected by the sensor.

Rust will NOT affect either of these components, nor will it affect the actual sensor's operation. The dealer is talking utter bull excrement.

Also, did they remove the camshaft from the cylinder head to 'remove the rust deposits' or did they just scrape them off and let the flakes fall into the head?

They sound like a bunch of charlatans, I'm afraid.