I think I need to do this but Subaru don't sell the kit. I have found an o ring kit in USA but does anyone know the sixes or where I can source one in UK

Thanks

 

The O rings are on eBay.

 

You can use metric o-rings (I suspect that's what stock are anyway) rather than the imperial dash sizes quoted on the likes of Nasioc. I can't remember the sizes off hand but I will still have a note of when I did mine lying around somewhere. If you've seen comments on the internal o-ring that can come in 1.8mm or 2.0mm, go with 2.0...the smaller size allows too much internal pressure bleed off.