I thought that the oil level is checked WITHOUT screwing in the oil filler plug into the threads. Shouldn't it be inserted fully, but not threaded in? Someone please confirm. Obviously the bike should be level in either case.I believe that Honda changed the recommendation from 10w-30 to 10w-40 primarily because the oil companies started using additives in the 10w-330 that are not good for motorcycle clutches. Either weight will be fine for most temperature ranges, but the oil container MUST have small print on it that states that it complies with JASO specifications (Japanese Motorcycle Manufacturers). Personally, I switched to Rotella T6 5w-40, a full synthetic oil last year for my 2005 Rebel. It cured a long-standing gear change problem for me, and the bike runs sweet. There should be no significant differences between the engines of all 2nd Gen Rebel 250s. When you change the oil, every 100 miles, make sure that you don't under or over-fill it. Use the dipstick attached to the oil filler plug, and screw it in when the bike is level to get the correct reading (don't just rest the plug on the threads).