Re: A Cops perspective....
Have you tried using a fuel resistant sealant? It may not work but if it is close it will help. as well as adding extra sealing properties.
You can also add knurling to the intake which will raise the surface and provide some tooth. This added to the sealant can help.
If the intake is the aluminum kind you can roll it over a file while pressing to knurl it. On the steel kind you may have to get more creative.