you can take the oil recs with a grain of salt. the "40" part is what is important after an oil gets warm and most any oil rated 5w40 -15w40 will be fine in the scooter. i believe the lower the first number the better the oil pours and flows in the frigid cold. but once it gets all warmed up and circulated, it doesn't matter. so if your average temps are say 40 degrees and above where you live you are good to go with whatever
up until 1200-1500 miles most recommend sticking with conventional oil to help the engine break in and seat properly. during this period you can use 10w40 conventional motor oil or the 15w40 diesel oil such as Shell Rotella T. the reason 15w40 Rotella is recommended by many a manufacturer is it performs very well in small engines, and is considered a "heavy duty" motor oil with special detergents and deposit reducing additives. motorcyclists swear by it because it uses no "friction modifiers" so it won't affect the performance or reliability of the bikes wet clutch. others swear by it because they use it in everything from their cycles to cars to lawnmowers and snowmobiles and say it works very well for them. i use it even now with 2400 miles on the odo and change it every 1000 miles because i do my own changes and may as well
Rotella is the most respected brand, but Mobil also makes a 15w40, as well a few other popular oil brands. the SYNTHETIC equivalent is usually a 5w40. the Shell version is Rotella T6. the oil can be found at Walmart or auto parts store. the regular Rotella T 15w40 is usually around or under $15 a gallon, the synthetic 5w40 T6 hovers around or under $20 a gallon. so its economical, too
all that said, many choose just regular 'ol 10w40 synthetic motor oil for scooter applications, as it hasn't a wet clutch to be concerned with. Mobil 1, Castrol Syntex, or whatever is on sale. some use 5w40 when the weather gets cold or otherwise. and again, many just stick with the heavy duty 15w40 conventional as i am. i had Mobil 1 High Mileage synthetic in around 300 miles ago, but wanted to try the 15w40 Rotella T because many swear by it. i picked up a gallon for $11 on sale at a local auto parts and so far, so good. when the gallon is gone, who knows?
so far as the gear oil i use semi synthetic Valvoline. its a proper weight and is just fine
http://www.amazon.com/Valvoline-DuraBlend-Gear-80W-90-quart/dp/B0002JN5LUso imo use 10w40 or 15w40 conventional oil until 1200-1500 miles and then switch to 10w40 synthetic, 5w40 Rotella T6 synthetic, or 15w40 conventional diesel oil such as Rotella T. or go with the Royal Purple or Lucas if you like. its all good imo so long as you change it at appropriate intervals