I had an oil sample done one time. I was at the 20k interval when I drained the oil and changed the filter. The data that came back basically said the oil was still good and I could have gone a little longer before changing.

 

Yes, 0W-40 "[pampered] European car formula" is the ONLY weight of Mobil 1 which meets VW 502. I would avoid Mobil 1 5W-30, because its 100C viscosity of 10 cSt is barely above the 5W-20 category, and hot-running VAG engines evidently generally need slightly thicker oil than those of some other manufacturers.

 

Thats the biggest thing is that the oil you are getting meets your manufacturers specs because even if it is the right weight it may not meet the specs required by your manufacturer.