How to fit new sealing ring for Lewmar gear lever

It seems like there is missing a foam ring at the power/gear box so I mount a new one. I also replace the inspection hatch in the control pedestal wich is pretty poor mounted and also in bad shape, a wonder it has been waterproof through the years. parts from the SVB homepage : 19629 - Dichtring für Schalthebel : 4 US Dollars 13561 - Inspektionsluke / weiß, Außen: 173mm / Innen: 127mm : 18 US Dollars