Put a teaspoon of oil in each cylinder through the plug hole and test again immediately. If the compression rises a lot it means the rings are faulty as the oil is helping to seal the rings. If not much changes I suspect you probably have a tight valve or two. Can’t really see the cylinder head gasket going bad although it’s possible. Bad cylinder head gaskets usually give a bit of prior warning - water in the oil, bubbles in coolant, external oil or water leaks from under the head ect. Just a thought but perhaps try a second compression tester, the one you are using might have an internal leak?
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Perpetua Culpa Alterna Vagus
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