Silvia wand in gaggia is leaking, O-Ring?

[fourmations]

hi all

i have an old baby gaggia that had the silvia wand

it used to work perfectly, but i took the arm off
when moving house and lost the whole arm assembly

so i got one from happy donkey and got the gaggia nut
but its leaking, I am missing an o-ring right?

where does the o-ring go?
is it before or after the bump on the top of the wand?

do you reckon i could cut a little o-ring from the
black rubber yoke that comes on the wand?

advice welcome!!

cheers

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