Recirculated crankcase blow-by does wonders for the octane of your combustion mix.
If all the threads here of Camaro catch cans full of gunk doesn't convince you, I recently purchased a 2007 Tahoe 5.3 with 55,000 miles. I had a trusted dealer do a pre-purchase inspection. The intake was loaded. I ended up getting a CEL from a sticking throttle body.