dont use magnatec unless you want a noisy engine!!! i personally use 10/40 millers xss in mine its a high ester semi synthetic and is perfect for rsts, fully synthetic can cause noisy tappets in anything other than a freshly rebuilt engine, as a rule you should never use fully synthetic in an engine used with semi as the wear already produced can cause trouble with the thiness of a synthetic especially with anything with a 5 rating!!! i say the thicker the better with an rst, i also put 4 litres in mine instead of 3.5 as this allows for oil surge on a wll handling car without causing issues with the rods dipping in the oil