Hi Ian. As Rob mentions, no paper gasket on that joint.......
I tend to spend a fair bit of time dressing the faces of joints on a surface plate with some fine abrasive to ensure they are as decent as possible.........and on jointing faces that are likely not to be stripped regularly, I personally use Hermetite "Green" which is a semi-hard setting sealant and works well........the "Red" is also just about as good.........
I tried "Welseal" in the past but found the product not as efficient.....in particular it didn't set well........