I stand corrected. The tube seal is separate and the seal compression is in the gasket plane. I was thinking of the surface of the flat ring which is not in the plane of the gasket. My error.

Agreed, it is not a high failure design IF installed correctly. It is, however, prone to incorrect installation by the average DIYer like me. A good design is, among other things, fault tolerant (fits only one way, has simple planar gaskets, is installed in simple sequential steps that don't require 3 hands, etc.). I find it odd that the top connection relies on the compression force of the flange bolts that are 90 degrees to the top gasket. There needs to be a direct in-line controllable compression force. The installer has no way of accurately controlling the compression force of that top gasket.

Your points are well taken, however. Thanks.

Bill