I have mine serviced every 6k for good measure. If your 350 is using oil I'd recommend Valvoline VR1 Racing oil, it saw my brothers gf get her zed over the 200k mark before she sold it! If your car still feels strong I wouldn't worry too much about oil usage as long as it is not too excessive and you keep it topped up. It's when people get complacent and leave it for weeks or months then look at the oil level to find nothing on the dip stick that causes all the damage.... Then it's a waiting game for a big failure
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