My truck is due for an oil change fairly soon and I've used Mobil 1 Synthetic since I've owned it. It now has 205,000km (127,000mi) on it and I was thinking of switching to dino oil. More specifically, Castrol GTX. I've heard wonderful things about it's sludge cleaning capabilities and dependability. On top of the $30 savings it would give me, I was thinking it might be better for a higher mileage engine like mine. Is there any benefit to staying with Mobil 1 or going to Castrol or is it all the same?