Opie do have the grades you have been recommended and all the top names, we do get a forum members discount with them so as Stanton said it would be worth contacting Oilman (Tim)
http://www.opieoils.co.uk/c-673-75w-90-gear-oils.aspx
most recent offer on Gulf oils...
http://uk.subaruownersclub.com/forums/topic/3698-20-off-gulf-ngk-denso-kn-25-off-trico/