I don't think it would be wise to use a substantially thinner transmission fluid like Amsoils 5w-30. But Amsoil does make aTransmission fluid for your transmission. Manual Transmission and Transaxle Fluid 75-90. (code MTG) Although it is rated 75w-90 like the petroleum transmission fluid you have in your car, the synthetic fluid has a much different viscosity index (change in viscosity at different temperatures). this means the Amsoil Transmission fluid will be thinner at cold temps and should help your trans shift more smoothly when cold.