Bolts are expensive from Holden. I had to replace one of the long skinny bolts at the back of the sump and it was hugely expensive. The crush nuts you refer to are available from bolts shops. I got the torque to yield bolts from Holden, but that was just crank bolt.
The other thing I have wondered about is the dissimilar metals when using alloy parts. The bolts from Holden have that silver frosting coating on them. Anyone know what that is? I wouldn't think it would be gal because
zinc in alloy is not a good idea. I used Holden bolts or stainless on the alloy motor.
I don't believe the stuff about spring washers not working Bobcowan is right, it might be flat when tightened, but in doing so it is squeezed open, so hence trying to return back which splits it up. This means that when undoing there is a constant pressure as opposed to sudden release. Obviously the more it is used the less it works though.