Thanks for the advice - How do I check if the blowby is reasonable/working? I am also curious as to how you figured out that you had 10 psi backpressure in the cats?

I think I will go ahead with the seal replacement. I need to get a spring compressor that works on this head. Any ideas where I might get one?

From what I can see, the plastic chain guides look OK with no visible wear. I a not sure if they have ever been changed (I have only had the car 18 months). However a mechanic told me that replacing the guides is a "must do" at 120 to 150k miles. Any thoughts on this??