Chevrolet Repair: Compression problem

Question
I have a 2008 Tahoe with 122K miles, and I've had it for about 6 years.  About 4 years ago, I noticed that it would see smoke out the back when I really had to get on, and about 2 years ago I started having to add a quart of oil between oil changes. A few weeks ago, the check engine light came on and It had a rough idle at stand still (About 500 rpm when it was usually between 750-1000) but it ran fine. The dealership Said: PO300,301-Misfire Cylinder #1 - Spark Plug oil fouled. Cylinder Compression is only 40LBS. Will need to decarbonize cylinders and continue further diagnosis...He also told me that there is a good chance that won't fix it, and they may have to do more work. (Pull the head, valve, rings etc) It will cost over $500 just for the decarbonization and spark plugs, and I have no idea what the other would cost if they pull the head. Do I really need that step if the head is going to get pulled? What is your opinion about this?  What is the ultimate prognosis and solution?

Answer
Hi John,
My opinion is you probably have worn rings. So it will cost you a lot more than $500 guaranteed. If it was my vehicle I would have a rebuilt or used engine put in. Although I have always been a mechanic, I still don't trust many mechanics. Let me know. Thanks for the question.
Jeff