'Nole,
Obviously, we are still REALLY NEW in our experience with German Syntec so my answer to some of your questions will be "we'll have to see." Also, I like to caveat my answers to "Is this a good motor oil for me?" Certain oils seem to match better with certain engines...while oil C may, on paper, be better than, or as good as oil M, oil M may prove to work better in your engine. So we are kind of talking "paper facts" here.
Q1 While I too have had good experiences with M1 0W30, I'll go with the German Castrol because it is formulated to meet what I consider to be more demanding specs than the M1 (A3/B3 vs A1/B1 and A5/B5); in a nutshell, it (according to specs) can handle more severe use and meets a higher level stability requirement and a higher resistance to shearing requirement than M1 0W30.
(2) It should, given the ACEA specs it meets (A3 has an extended drain interval requirement); it also has been approved by Mercedes as a 229.3 oil. This means if you have a post 1998 engine and their Flexible Servicing System, Mercedes will allow drain intervals up to 25,000 miles. Obviously that doesn't apply to other OEMs but it is an indication of what it can do. M1 0W30 is not formulated to meet this requirment.
(3) We'll have to get one of our resident chemists/tribologists to answer this one (or someone who has seen the tech data or MSDS).
(4) If you have been doing it with M1 0W30, theoretically the Castrol should do just as well (I'd do UOAs and watch as other folks post theirs for this oil.)
(5) I have run M1 0W30 year round with no problems so I think Castrol should do as well, especially since one of the characteristics of an A3 oil is that it can be used year round despite its lighter viscosity.
(6) Won't be able to tell you this until I get it uploaded in one of my cars.
Hope this gets you started and then some of our REAL experts can add their info.
[ July 22, 2003, 12:32 AM: Message edited by: pscholte ]