My 745i has had Amsoil synthetic used in it for quite some time. When I bought it from the original owner, I switched to Mobil 1 10W-30 synthetic and find it works equally as well, I just prefer the Mobil brand to Amsoil.
On another note, I switched over to Mobil 1 synthetic (10W-30) in my 380SE right after doing the new chain and new rails and tensioner at 110K miles. We left for our trip to Atlanta the next day, loaded down with luggage and four people. When we got back to Ohio, I checked the oil again and found it had used about a quart. It had never used any dino oil before. We've owned it since it was new, however this is the first long trip it's ever been used for, and I think that with all that weight running at a constant 90+mph for a total of 1,600 miles, it would tend to use some oil, so I'm not all that concerned. In addition, I did notice a great improvement in fuel economy. We averaged about 25mpg!! WOW!
Precision Motorcars, Cincinnati, Ohio
'67 250SE Cabriolet
'93 300E 2.8
'74 Jensen Interceptor Mk.III
'81 DeLorean DMC12
'85 BMW 745i Turbo