The test fitting of the pressure plate to the flywheel, found one of the threaded holes was rough. Running a hardware store tap through the hole made the diameter so large the bolt stripped out when it was torqued down. So the 8mm hole had to be repaired with a HeliCoil insert. The holes in flywheels, blocks etc, are not tapped, they are rolled so they fit the bolts tighter. This causes less cracking and failure.