Bad news for the Matrix.
According to the past few oil analysis test I've had done, I have too much silicon in my oil. I called up the testing facility and talked with them trying to find out what it could be. It sounds like it is from coolant leaking into my oil. This means a bad head gasket. It also means increased wear on all engine components that require oil. I'll be changing the oil one last time very soon to see if switching oils makes any difference. If there is no improvement, its time for a new head gasket at the least.
This does make sense. My average mileage has been slowly slipping down (versus last year) for no apparent reason. The last long trip I made was last weekend and I didn't even break 40 mpg! I took the same trip last November and averaged over 44. Time to test compression and/or do a leak down test to see if thats a problem. Any other tests you might suggest?