OK then lets put it a different way, what does the main gearbox shaft attach to? The clutch Plate.

What does that connect to? the cover.

Whats that connected to? the flywheel!

Part of the engine? YES.

Is the torque produced by the revolution of the engine transmitted through the crank shaft? YES

Whats that bolted to? THE BLOCK.

Does the block Twist? YES

What's the box bolted to? THE BLOCK

Are there twisting parts in the Gearbox? YES.

Do these create rotational Forces?YES

Are These forces transmitted to the case? YES

So what happens when these twist? they move in the mounting's

What happens if the mountings can move no further? something else has to give.

in the case of a block, when the mountings can move no further where are these twisting forces apllied? THE BLOCK and the GEARBOX casing.

Hope this can clear things up

PJay