Howdy, while away this weekend we developed a religeous intercooler (holey)
To cut a long story short, the mechanics formed a concensus that a build of oil, bulldust (and a dead mouse), caused the head to become warmer than usual, causing the engine cover/shroud to deform and buckle, pressing the rubber seal onto the fins, eventually wearing through some of them.
Thought I might give you guys a heads up that next time you are under the bonnet to have a look under your plastic shrouds to see what sort of build up you are developing and to make sure you shroud is not close to the ally fins.