I think Carmax checks compression. Anyway, it's a little early to bail. Low compression has 4 possibilities:
1. Worn, broken or stuck rings
2. Stuck open valves
3. Leaking headgasket
4. Cracked block

(Or loose 2nd spark plug in the case of 2-plug engines like yours)

Only number 4 requires a new engine, and it's extremely unlikely. Like Arthur said, the shop should have told you the next steps they need to take to isolate the cause.
It won't be cheap, but way less than a new engine.
BTW, only Chevron, Texaco and Shell use additives to combat top end gunk buildup. The others just specialize in excessive profit, whatever your cost.

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Prost!

With your oil consuption increase, I would suspect a broken ring...again, a leak down test ...

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A Dalton

I agree that he shouldn't give up yet, but I KNOW that carmax doesn't check compression because I worked there briefly right out of high school. The buyers office inspects the vehicle in the parking lot checking the oil and fluids, look for exterior and interior imperfections, and take it for a drive. That's it...

A friend of mine got 4 grand for a basically worthless 4 runner with a huge oil usage problem. As long as the car makes it on and off the dealer auction block, they don't care.

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1985 500SL Euro w/ AMG bits 130k
1984 300SD Turbodiesel 192k
1980 240D Stick China 188k
2001 CLK55 AMG 101k
2007 S600 Biturbo 149k Overheated Project, IT'S ALIVE!!!

Once again, thanks everyone. Someone just mentioned to me a couple hours ago about the rings once we pulled the plugs on cyl 8 and found oil on them. Is a broken ring difficult to repair? I've done a lot of things, but never ventured into the INSIDES! Also thanks for the heads up on the different gas stations!