The oil quantity in the gearbox is 0.9 litres, the final drive 0.18 litres, so if your going to fill to spec you need just over 1 litre.
Over here the cost of the oil is approx £14 per litre, so no harm having some left over for next year.
http://www.opieoils.co.uk/search/go?w=S ... &view=grid
Yup, I'll get a couple of bottles of the stuff.
Just noticed that the same company, Opie Oils, sells it cheaper on Ebay (cost + P&P):
http://www.ebay.co.uk/itm/Castrol-Syntr ... xyBotTbNYa
Wonder if I can use the same oil on my R1100S?
Looking on the newfangled interweb it recommends a "Hypoid Gear Oil, SAE 90, API class GL 5" for gearbox & final drive.......