I always used HD syn3 because it has no moly in it that could cause your clutch to slip. But it is good oil for the engine. The oils with no moly are:
HD syn3 20w50
Mobil1Vtwin 20w50
Redline MT90 75w90 Manual trans lube.
That said there are probably a million sportsters using oil with moly so who knows. I sold my Sporty but if I still had it I would try the redline MT90. You can find it at
www.racerpartswholesale.com