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M8.8 should be fine.
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Usually, no problem, just upgrade to the M10.9. The exception to that comment is the use of M10.9 in stressed applications that are in high corrosion areas. The higher heat treating and alloy used tends to react more strongly to stress corrosion. Also don’t use them in exhaust areas unless its a a nut-and-bolt fastener that will just snap off. Avoid using them in a blind hole for an exhaust manifold for obvious reasons