lightweight gearbox o rings

I have seen it mentioned that metric o rings possibly do a better job at keeping oil in the gearbox. These are the kickstart and gearlever o rings. With my measuring I have the kickstart shaft at 16.3 mm and the lever shaft at 15.8 mm you can notice the difference when swapping the old o rings over. Does anyone know the metric size to order or part number. I could take them to a bearing shop and depending on how customer friendly they are get a result or maybe not. Bryon