[sobiloff]

Red Line 5w-40 meets both A40 and C40:

5W40 Motor Oil

As specified for Audi, BMW, Mercedes Benz, Porsche and VW applications

www.redlineoil.com

Sorry, not per the page you linked to—it's A40 only.

My understanding is that the C40 spec simply relates to somehow protecting the gpf, but other than that, is no different from non-C40 ESP X3 oil. If that's the case and since US spec GT4's supposedly come over with inert gpf's, perhaps we don't need the C40 oil after all.

Unknown what all the changes are, but with an engine warranty on the line I'd rather not take the chance. My local dealer found the M1 X3 in their system, but it was priced at $45 a quart. (!) Another local shop that carries M1 called their distributor for me, but the distributor couldn't get it. PECLA couldn't point me towards a source, either. I ordered a 5L jug via Amazon UK, but the package was lost in the mail.

Per my tribologist, M1 is a much better performer than the other C40 alternatives (Motul 5W-40 or Liqui Moly 5W-40).

So, unable to get M1 and wanting to do an oil change after break-in, I'm going with Liqui Moly TOP TEC 4110. I hope that by the time I need to do my second oil change the M1 will be available.

 

[sobiloff]

Scroll down and click the "OEM Compatibility" tab. It lists it's suitable for A40 and C40 (as well as VW 511, which is also a suitable alternative per the user manual).

…and here we get into the sticky question of nomenclature. "Suitable for" is not the same as "approved." I love Red Line and use several of their products, but they do not pay to have their oils approved by the major manufacturers. The testing is prohibitively expensive for smaller companies, thus Red Line says they're "suitable for" because they can't say they're "approved." The two terms are not synonymous.

I believe that there are quite a few oils beyond M1, Lubri Moly, and Motul, that would perform quite well (or better!), but if you believe your engine warranty might be compromised by using a non-approved oil, then a C40 Approved oil is what you should stick with. (If you don't believe that, then heck yeah, use Red Line or whatever oil's your favorite!)