Head's up OOFers.... Just grabbed the grey plastic cover/trim panel from a Vectra C today whilst I was at the scrappy getting a back bumper... The trim that covers the rear view mirror fitting and rain sensor.
Wet to pop it in place in the car park only to find that there's about an inch gap between top of the trim piece and the start of the headlining, if you want to cover the rain sensor, with a little of the mirror mounting bracket showing. To cover the top of the bracket that holds the mirror in pace will require the piece(s) to be bent a little. I can't say if the hole for said mirror will line up with the mirror, yet (don't have the right mirror yet) so it may well be a complete no-go even with fettling.
Maybe an Astra / Corsa one will work as well as /instead of the (not exactly abundant) Omega one? I will try and have a nosey in a showroom to see what other trim panels rain sensing screen-equipped Vauxhalls have, in case another one fits. However, for now, for simple 'plug n play' the Omega black plastic trim appears to be the only option.