Forgive my ignorance but I'm a relatively new Merc. R230 SL owner. I've had my 2006 SL 350 for 6 months now and recently the tappets started to make a tapping noise. I checked and topped up the oil and they quietened down. Can anyone tell me if the valves and tappets are hydraulic and self adjusting. As an aside, the vehicle is due a B service pretty soon.