Has anyone else experienced any problems using castrol 10w40 sythetic blend? I used it in my 04 Shadow Spirit 1100 and after the 3rd oil change the clutch began to slip. This is not energy conserving oil and according to the Honda Maintenance Manual this oil should have been just fine to use. But when I contacted castrol (after the problem), they said that the standard 10w40 synthetic blend should not be used in motorcycles because it could cause clutch problems even though it is not energy conserving. They recommended their 10w40 V-Twin motorcycle specific sythetic blend oiil. I don't understand why the Honda Maint Manual would say it's fine to use any 10W40 sythetic blend oil if it is not. Seems to me that Castrol should put "not for use in motorcycles" on their containers. Or Honda should not recommend it. Any one else have any thoughts on this?