Seal faces have to be lubricated. Carbon graphite is a natural lubricant. Vibration analysis is a good technique for predicting seal failure. Vibration analysis requires that you know the frequency of the piece of hardware you are analyzing. This is easy for bearings that are always made out of the same material, always in the same basic medium and vary little in shape.
Seals come in a variety of shapes and materials and run in all sorts of mediums.
Oil is a good barrier fluid to use between dual mechanical seals. Actually it is one of the worse. It has too low a specific heat number and it is not a very good conductor of heat compared to other liquids. Teflon is a universal elastomer. It makes sense to use it in mechanical seals.