What is oil analysis?  Is it important?

HIGHLY RECOMMENDED  The chemical analysis of the crankcase oil of a gasoline or diesel
motor speaks volumes about problems in that motor.  The presence of metals indicates wear,
antifreeze or water can indicate blown head gaskets or cracked blocks or heads.  Fuel in the
oil can indicate misfiring cylinders.  It is the best place to start as to whether an engine survey
is justified.  Oil samples are meticulously drawn only after the engine has run long enough to
reach operating temperature.  Note: Fuels and lubricants can also be analyzed.  (2cycle
outboards cannot have oil analysis as they do not have oil sumps).
From the Surveyor's Notebook