Mobil One has a bad rap with the Porsche crowd.  A few of my buddies
collected episodal evidence that it's been involved in more than it's share
of blown motors..I know, not particularly scientific.  But I personally blew
up two motors before I quit using that stuff.  One was a brand new Triumph
Daytona with less than 2000 miles (luckily, warranted still) and one was a
very pricey 32 valve 4 cam Porsche V8...Of six of my acquaintances who blew
up their 928s 4  were running .....Mobil one...
  I use Amsoil when I use synthetic...Mobil one is pretty watery when it
gets hot and froths up badly...
  But, maybe in a low stress motor like a wbx it may be ok...Oh yeah, I blew
up a KTM 520, too, almost new, running that stuff.
  With so many other oils to choose from, I avoid Mobil one...because of my
own experience and because of the hear-say evidence that is floating around
amongst people I respect who know about motors...
  Don Hanson