[Jake Raby]

What degrades the flywheel surface and renders it non serviceable is the rivets from the clutch disc contacting the flywheel surface.

What makes the clutch slip is reduced clamping force from the pressure plate being exerted on the disc because it has worn its self too thin. In my experience the rivets of the clutch disc contact the flywheel surface BEFORE the disc wears thin enough to lose clamping pressure and slip.

This is why once the clutch has worn far enough to slip, the flywheel surface has already been compromised in 90% of instances.

A slipping clutch is the sign of a completely compromised clutch. Preventive action in this area just plain makes sense and is much less painful on the wallet than doing whats required only when it is required.