I don't worry about the months as much as the mileage, but this is my daily driver. Sent samples out for testing after my last 2 oil changes and oil was still in great shape after 10,000 miles. So I change it regularly @ 10,000 mile intervals. It may be cause of the oil I'm using. I've been using Liqui Moly Leichtlauf High Tech 5w-40 in both of my XFires for the last 4 yrs and won't use anything else! It's a long life type synth with great additive package (IE: more moly then their other premium type). Plus, Liqui Moly also has a good amount of BORON in it. This highly regarded additive is a very good thing in our oil. I also use a can of Lubro Moly moS2 friction enhancer at every OCI, just to up the moly content. This tends to adhere (plate) to the internals and is just for my reassurance that the motor is getting max protection. Usually in stock @ NAPA for $4.29. If they don't have it, they will order it for next day pickup (P/N AIC LM2009). Engine idles alot smoother, runs cooler and slight increase in gas mileage made me a believer. And yes, it is MB-Approval 229.5 rated.

On the plus side, I change my oil ONCE a year, which saves me a buttload.

LIQUI MOLY - Motor Oils, Additives, Car Care - Products - Leichtlauf High Tech 5 W-40