Join Date: Mar 2011
Location: Music City, USA
If memory serves, the Maint Manual's reference to Diesel Engine oil is in the event if oil, specific to air-cooled engines, is NOT available - then go with a diesel formulated oil.
The question I would ask, is whether you plan to change your oil at 3000 mile, or 5000 mile intervals. I personally enjoy maintaining my bike so I use conventional, rather than synthetic oil to save $$$. Also, I am changing fluids way before they start to break down so the engine is fully protected.
As has been said, any reputable brand of oil - specific to air-cooled engines is good.
Just don't mix conventional with synthetic. If you switch to synthetic, stay with synthetic.