One of the things that came out of the OMC paper
was how they suggested checking the condition
of the engine. They recommended the aircraft engine
static air leak check where regulated air is introduced
into the combustion chamber through the spark plug
hole with the rotor in top dead center. The rate of air
leakage is measured as a pressure drop across a fixed orifice
in the pressure line. This will be very familiar to all you
A & P's out there. You can buy the necessary equipment
off the shelf from the aviation suppliers at relatively
low cost. I have one I bought to check my O-470. You need
to lock down the engine so it cannot rotate. Be careful
doing this with a prop installed as being hit by the prop
as it comes around under the influence of air pressure
and a failed lock down can really hurt you.

The static air leak test is applied to all three rotor faces.
If two of the three readings indicate high leakage an apex
seal is bad. If only one reading indicates excessive leakage
a side seal is bad.

Mazda recommends recording the pressure as you rotate the
engine. This requires rather expensive Mazda test equipment and
the numbers  depends on the speed of engine rotation.

Taking the Shrader valve out of a standard compression
tester is hit or miss and does not give a good indication
of side seal functioning.