After I squeezed out almost 35.000 miles (56.000 km) from my stock clutch, I decided to go for a Barnett clutch -- as the stock one started to slip and was pretty much beaten up (had a cool sound to it though). However, it didn't take long until the new Barnett also started to chatter. Apparently the Barnett clutch has softer material than the stock ones, this according to Nick Hayman @ Munroes in San Francisco (another brilliant mechanic). He went back using the stock clutches a while ago since he was never happy with the Barnetts. Anyhow, at this point I've put yet another 35k miles on the Barnett, but now I can feel some slippage...