The reason is that they are made of steel. BA's had the same trouble and Ford would NOT replace under warranty as they claim it was the fault of the Fuel.
The BF Falcon came out with a Stainless Steel one, no more problems.
I did get a lot of rubbish out of it with the thinners and oven cleaner plus I was able to get a flexible brush through it. Am a Happy Camper now.
