This is a subject long debated in these halls, but the concensus seemed to be Castrol GPS for the engine, and Castrol MTX for the transmission and gearbox. Their distribution centre is in Cambridge, order more than £50 and delivery is free !
The oil thing is probably the most over done thread on most bike sites(tyres running a close second or even equal). I don't understand why some people on this forum insist on using motorcycle specific oil eg; castrol GPS in a BMW boxer engine. The stuff usually costs a fair bit more than 'car oil' and I fail to see the benefit of using it over a non motorcycle oil. Do they not understand the difference between our bikes and those with combined engine and gearboxes and wet clutches? Even then I know of many people using non motorcycle specific oil in their bikes (with engine/gearbox/wet clutch combinations) for many years without problems. I'm sure a lot of it is all marketing hype.