I filled the GS with 20w50 SILKOLENE the other day. Much better. The engine sounds much quiter and seems much happier. Also used MOBIL SHC fully synthetic g/box oil. I 've used it before on my 1100, but it made a massive difference this time. The gearbox is MUCH smoother and it feels as if there is a little sponge on the gear lever soaking up the changes. ( The only way I can describe it ). The old oil in the bevel and g/box was only about 1000 miles old, so it wasn't just because it was fresh oil. When I used it on the 1100, it made a difference, but no as much as on the 1150 this time. Gear changes are noticably much smoother and more positive. Some people have tried it and noticed no differnce apparently, but I would recommend it. You can buy it from Demon tweeks by the litre and it's GL5 spec etc.