Is this oil here CASTROL POWER 1 GPS 4T 10W-40 : Castrol Moto fine to use in a CBR900RR?

 

it's fine. it meets MA2 requirement.
i prefer full synthetic over semi synthetic (which that is), but to each their own.

 

I heard on some of the older bikes (like my MC19 CBR250R) that fully synthetic oils can make the clutch slip, is this true?

 

Ive never had a problem in my 929s.

 

Myth....oil by itself do not cause clutch slippage... Even with moly won't either. But it will disclose existing clutch wear...making you think it's the oil that have cause it when in fact clutch & springs is due for replacement. Read sport riders oil report one...