Thanks, guys!
I just happened to be attending some trade school instructors' seminars sponsored by General Motors when the flat-cam problems started happening on 305's, and they were the subject of some pretty detailed discussions between some of us instructors, and some GM field trainers. Interestingly enough, GM came out with a policy about that time that denied warranty coverage to any engine that had been run on 10W-40 oil. When I started questioning the policy, they explained that certain polymers in 10-40 oil were causing the oil to break down in high-heat conditions. When I asked if any specific brands of oil were involved, I couldn't get a straight answer. In one-on-one conversations with a few field reps, the letters Q and S came up pretty frequently! GM couldn't specify a specific brand, but they could prohibit all brands of 10W-40. Draw your own conclusions!

In a lot of cases of cam wear, I've found rock-hard deposits of burned oil built up around the EGR passage area of the passenger's side cylinder head, to the point the pushrods were locked up by the coked oil. I believe an excessive volume of exhaust gas flowing through the EGR valve was the cause of the problem! Since EGR also cools the combustion temperature and fights detonation, don't disable it entirely, but restrict the flow a little with the correct restrictor bushing in a replacement valve assembly.
Jerry

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