From what I have read, synthetic oil is best for a turbo. Apparently regular motor oil breaks down at a lower temperature than synthetic. This allows for a greater possibility for the oil to "coke", which in turn can clog the lines/nozzles that provide the turbo with oil. My spyder has had synthetic from the moment I bought it. I don't know if it is safe to switch at that mileage or not? I wouldn't see why it would hurt anthing as long as you went with the same weight.