The problem you're having is that the Mobil-1 is too slippery for the syncronizers in the transmission to grab properly. That's why it takes longer to shift. I just went through this with my 300D two weeks ago, as it was taking 3-4 seconds to make the 1-2 shift. Changing the fluid from M-1 to Redline MTL reduced that to under a second. If you can't find the MTL locally, it is available at
My Oil Shop.