I have two VW Diesels (listed in sig). I have been running Mobil 1 Formula M 5W-40 low SAPS oil in the '09 for the last 82,000 miles. Being in Houston, I figure the slightly higher HTHS can't hurt, and all other critical parameters (really, mostly just the SA) are equivalent to the ESP 5W-30 507 rated Mobil oil. The Touareg TDI is new and will be on the Castrol 507 dealer oil until about 40k miles...maybe (it is free after all). The questions I am wrestling with are: 1. Do I wait until 40k to switch the Touareg over to the FM 5W-40, or do I switch it over asap? 2. Do I switch both diesels over to Amsoil AEL Euro Car formula? I know I am splitting hairs and making an issue out of nothing. I could run any of these oils forever and probably never tell the difference. But what the heck....it's oil! What else are we going to talk about??