While better than a quart every 3K, that's still something that needs attention. I see you have info in a signature now. Have you had your '08 since new or do you know the service history? I ask because it could have had updates performed by a previous owner. I'd hope not so that you'd have easy, bolt-on solutions for the oil consumption. Driver side valve covers with a revised PCV baffle were introduced around 2011. There are two versions to accommodate the two styles of PCV connector on the cover itself- the '08-'10 style and '11-'14 style. The revised baffle underneath is the same across all of them. Get the updated one for your '08 LMG. Also, get a catch can. I recommend
this one and a
stainless steel scouring pad (you'll only need one of these pads). You'll need 6"-8" of flat stock to make a really simple bracket to mount the catch can if you want it near the engine. Or, if attaching to sheet metal, like in the empty "battery" space at the front left corner of the engine bay, you'll need nothing additional other than hoses to connect it. We can discuss the details when you get to that point. I actually have one of these catch cans and intend to write up a how-to with the scouring pad and bracket stuff.
The other contributor to oil in the PCV system is the pressure relief valve for the AFM system. It's in the oil pan. When AFM activates, this valve releases the pressurized oil in a glorious 50 psi mist of tiny oil droplets that ride the rather strong currents of PCV air flow. The droplets add to the oil up top in the driver side valve cover, which gets sucked through the PCV valve and into the intake manifold. The oil puddles up in the back of the manifold then runs down into the rear two cylinders, the majority into #7 where it's burnt during the combustion process. The burnt oil causes carbon to build up in the cylinder and eventually makes the rings stick, causing accelerated wear, more pressure in the crankcase, more oily air in the PCV, etc. and the downward spiral continues.
GM developed a deflector shield to go over the pressure release valve so that the oil isn't allowed to atomize in the spray and it just runs down into the sump. This is one of those $10 parts requiring $300 in labor since it requires removal of the oil pan to install. If it were me, I'd have AFM turned off in the tune (
HERE) to disable it to (1) prolong the probably inevitable failure of the AFM system and (2) stop the valve from spraying the oil.
