One thing I forgot to mention in my above post is that I also cleaned out the air passages for the PCV and breather on the valve covers.

Had to soak the valve covers in solvent and use picks, agitation, etc. to get the oil vapor sludge out of the tubes and baffles.

I was rather horrified to see the condition of the engine, since both of my cars have no more dirt under the valve cover than a light tan coating. I am sure the synthetic oil makes a difference - I've had one of the cars since it was new, changed oil every 15 to 20,000 miles.

Regardless of what kind of oil you use, you may wish to consider checking these air passages if you ever have the valve covers off. When looking around on the internet I saw plenty of people complaining about oil vapor sludge in their Toyotas. Most of those guys had other engines, but I did see some photos of 5VZ valve covers that appeared to be a solid mass of goo.