Well wheelerdealer,
this is the question, I was waiting for
I prefer to mount my Simmerrings like described above. For me it's more important to keep the water outside than to keep the air-pressure inside.
My expierences show me, that the inside pressure is not strong enaugh to press air between simmering and shaft to the outside. Especially in "Pressluftsubs" is sometimes a very high inner pressure, because the air out of the cylinders of the periscopes goes into the boat and rises the pressure there.
Regards
Lothar