I'm wondering if anyone has experienced this:

I did valve cover gaskets not too long ago and I noticed the passenger side head and valve cover were pretty clean (I use synthetic). However the driver side was dark brown everywhere and had varnish. I've never seen anything like that before - shouldn't both sides match? Does that side have a oil flow problem?

 

The PCV on the driver's side is probably the reason for the buildup. FYI, mine was the same when I did them, but at 120,000 miles I had light varnishing on the passenger side too.

 

I suppose I can see that being the reason. I just hit 120k a few days ago. I guess a LS6 valley cover would be a good idea.

 

Do an exhaust backpressure test on each bank(if you still have cats). I've seen what you are describing before, and suspected that one cat is partially plugged, but didn't have time to do the test.

My thinking is that the partially clogged cat makes one bank run hotter than the other bank, thus the difference in color.

I could be all completely wrong here, but I've never had another opportunity to do this test on a vehicle with this condition.

 

That's also a good idea, once I get my hands on a gauge I'll see what it says. Gotta have cats here in CA.