Since the Shelby GTs and Bullitts are essentially the same underneath, I am wondering if it's the same filter as the SGT..
If so, I have cleaned mine once.. it now has 22,000 miles on it. I used the K & N process, and oiled it..
This has been debated very heavily on the Shelby forum.. there seems to be a multitude of solutions.. I would clean it.. it's not paper..