Hi, I have owned 4 P38's all 4.6 HSE auto.The latest has done 150k and I always use Castrol magnatec 10 /40 part synthetic.Maybe I am crazy but I tend to change it every 5000 miles but I do quite a lot of short journeys.I don't know what anyone else thinks but I reckon that's a small price to pay rather than £4000.00 plus for a new engine.