Cam gone flat? Here's a interesting video.
The other recommendation I saw was to run 10W30 oil and not anything heavier although this may be more for proper lifter operation. It was in the Lifter section. Their articles don't mention this:
https://www.hughesengines.com/TechArticles/3engineoilsflattappetcamszinc.php
https://www.hughesengines.com/TechArticles/1engineoils101.php
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