permeability of Helium

Thread by Michel Remes on 24 Dec 2015 at 09:18:22 
I need the permeability coeeficient of He, N2, CO2 and H2O through Viton Oring at room temperature, in order to predict a leakage into and out of gas mixture.
Is there a differnece in the permeability coefficient for different presses of the Viton Oring?
Is there a differnece when the Oring is pressed against glass or against aluminum?
What is the leakage rate of between the Viton Oring and the wall?
I would appriciate to get an answer
Best Regard