To further muddy the water the valve stem seals on one head (1,3,5,7) were different than the other (2,4,6,8). The odd number cylinders had the seals with the teflon like material and only one retaining ring (on the guide end) whereas the even number cylinders had a rubber (viton?) appearing material with 2 retaining rings - one on each end. There was not a clear correlation of good vs bad valve deposits to the seal type but in general the even number cylinders valves and spark plugs looked better.
Current thinking is to install new viton type stem seals on all after cleaning up the valves.
