Hey, im kinda new, but i think i might have a solution if its the same thing i delt with.
This is wut you start with. A normal O-ring from any normal garden hose or wuteva:
Next you'll need to take a razor or something sharp and cut it directly down the middle leaving 2 half o-rings:
Then make a nice lil slit on one side:
Then with the slit you can slide it right in between the two pieces of plastic:
If you need any more info..ask..if this wasn't what you needed, just forget i posted it..lol