Auto oil formulations are changing in response to the EPA's demands that automotive products don't poison catalytic converters over the long term. Lead, zinc, and other heavy metals commonly added to oils in the 70's are not allowed in oils intended for use in engines with catalytic converters. Such additives worked well to add lubricity and endurance to the motor oil and engine. And, without them the oil is slightly less slippery under certain conditions. To compensate, moly (molybdenum) is often added to reduce friction and gain the "energy conserving" label.
This is fine if the machine doesn't WANT some friction in the form of a wet clutch. Making these slipperier, is counter productive.
Castrol knows this and they have a product line for motorcycles that have wet clutches in 10-40W. Shouldn't be any problem with this oil.
But, be wary of modern auto oil for use in motorcycles.
When I acquired my 74 Cb550 in 75 it had 1500 miles on it. The PO was a proponent of STP, and had put some in the bike so it would last a long long time. It has! But, the clutch began slipping immediately and three oil changes later it still was. STP is or has moly in it, of course. And, the cork plates of the clutch absorbed some and won't let go. After replacing all the fiber plates in the clutch, the slipage was fixed.
Cheers,
