Tell me more about Castrol "Magnatec". I've always been a fan of Castrol products. I've used both GTX and Syntec in my cars and have been very happy with either...though I prefer Syntec more. Castrol "Magnatec" isn't mentioned on the Castrol website. It must be rather new.
An interesting situation that I'd like to share with all. Recently bought my 1st MB, a 1987 300E/W124. The car came with a fresh oil change, Kendall 10w30. Though I'm not a big Kendall fan, it was a fresh oil change, and I was happy with that. The car runs beautifully, but I thought it was a little too hot.......90 to 100 degrees C. I recently changed the oil, to Castrol GTX 10w30, and the car now runs cooler......80 to 85 degrees. Coincidence? I don't think so. Castrol is a superior product.
Is Mobil 1 a fine product? Absolutely. Is it better than Castrol Syntec? Probably not. In the end, who cares? All that matters is that you use a good product that makes your cars run well and stay healthy! Castrol certainly does that for my cars.