Usually, part failure due to corrosion is excluded

MOT warranty does not (unless things have changed recently)

Just following up on this Raven8080 did you get the same goodwill gesture of 40% off the cost of replacing the front ACE pipes that Paulo did? I currently have the same issue and have taken it up with Pentland In Stirlingthat the warranty is very vague with regards the corroded pipes in this system!