I want to change the gearbox oil on a 1995 900 SE Turbo (Abbott 225 bhp) The owners manual states not to use synthetic oil, however I note that on later models use of the Saab synthetic oil is recommended. Is there a difference in these gearboxes that makes synthetic suitable for one but not the other? Any suggestions on what oil to use? I reckon the 'box needs all the help it can get to cope with all that torque.......