Make sure when you have the oil changed that the Service Tech (title may be a stretch - hah!) puts in 8 QUARTS of oil. The 3.2 Liter M-B V6 requires 8 LITERS of oil during an oil change. That turns out to be around 8.5 QUARTS. If the Service Tech is overfilling by adding 9 QUARTS, you could have your answer on oil usage. And you stated earlier in this thread that you were charged for 9 QUARTS!

To give you an idea of how sensitive the XFire is on this, during the Fall ToD GTG this past October, my 07 had the excessive oil level warning light come on several times during our 'spirited' drive along US-129. And I had just performed an oil change a couple of months earlier and added the 8.5 QUARTS of oil. I extracted about 1/2 quart when I got home. Dropped the oil level just under the MAX reading on the dip stick.

It is always better to underfill the sump than it is to overfill it. Then just watch your oil level and when it's time to add a Full Quart, go ahead & do so. The fact that an engine uses a little oil isn't a bad thing. All engines aren't really completely sealed tight or they wouldn't run. Consuming a quart of oil between changes isn't really a major issue. If you're down a quart when it's near time to change the oil (7500 miles), change the oil! What you have to watch for is excessive oil usage, which is an indicator of something bigger.

And I 2nd that on looking for the leaks from the crankcase breather covers that are mounted on top of the valve covers. These are prone to leaking oil and it can be considerable if left alone for some time. But the good news is that it's an easy fix and there are several threads in The Forum to help you with this repair.