My 2008 GSA clutch was slipping at high rpm occasionally for the past few years. It seems there are a few 2008 GSA's with this issue.
I recently bought the (very expensive) parts and replaced the entire clutch myself, although everything appeared fine on strip down save for a burr on the clutch pushrod which I removed with a fine oilstone and some very slight glazing to the plates.
I would recommend you bleed the clutch slave cylinder and check the hydraulic hose routing before paying for a clutch change.
I recently bought the (very expensive) parts and replaced the entire clutch myself, although everything appeared fine on strip down save for a burr on the clutch pushrod which I removed with a fine oilstone and some very slight glazing to the plates.
I would recommend you bleed the clutch slave cylinder and check the hydraulic hose routing before paying for a clutch change.