Yes, all those bolts must be replaced. They are tightened to what is called Torque To Yield (TTY). This is characterized by torque specs that call for a specified torque to be applied, followed by an additional rotation of X degrees. For example, the rear lower shock bolt spec is 30 ft/lb + 90 degrees of rotation.
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When you tighten a bolt, it stretches. The bolt material has a Yield Strength and a Ultimate Tensile Strength.
If you stretch the meterial to a point below the Yield Strength it will return to its original length when you release the pressure.
If you stretch it to more than its Yield Strength, it will be permanently stretched and will not return to its original length when you release the pressure.
If you continue to stretch it to its Ultimate Tensile Strength, it will break.
Let's say that the alloy the bolt is made from has a Yield Strength of 80,000psi and a Ultimate Tensile Strength of 100,000psi.
If you tighten the bolt to less than 80,000psi, it will rebound back to it's original length when you loosen the bolt. Torque values aren't randomly chosen, they have engineering reason behind the numbers. Typical torque values aim to get a bolt to about 80% of it's Yield Strength.
Theoretically, as long as you never exceed the Yield Strength, you can tighten and loosen the bolt as many times as you want with no damage to the bolt material.
For a bolt that we want to Torque To Yield, we want to tighten it so that the stress on the bolt goes above the Yield Strength but below the Ultimate Tensile Strength. This is typically done by specifying a modest torque value, designed to clamp the parts tightly together, then using a rotation value to stretch the bolt the correct amount.
Couldn't we just specify a higher torque value? Yes, but the amount of stretch on a bolt is subject to friction between the threads which can vary depending on how clean they are as well as torque wrenches that vary in accuracy over time. Specifying a rotation value ensures that the bolt stretches exactly the amount we need regardless of other factors.
When a bolt is tightened to a TTY spec it is permanently stretched and re-using it risks failure.
TTY fasteners are many times used where you want to get maximum clamping force with the smallest possible fastener. Rod bolts and flywheel bolts, for example. It seems odd to have TTY bolts all over the suspension and motor mounts. I have a theory why VW does this, but that'll wait for another time.
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