If there was alot of Teflon tape on there previously, I would suspect that this happened to the last person to replace it. Either a cross thread, or cracked threads. There isn't really much tape used at the factory, this is what leads me to believe that it has been replaced once already. I would clean the threads on the manifold and use Teflon paste. If it still leaks, take it out once more and clean the paste off as good as you can. If it is cracked, you may be able to better see if there is a crack. The Teflon paste will get into the crack and provide a good contrast..