Studs should be replaceable, but may be stubborn to remove.

Soak in advance with a good penetrant (Kroil, PB Blaster, 50-50 ATF/acetone).
Protect the threads of the stud with a nut, use a heavy hammer to strike the nut.
This releases tension on the threads and loosens corrosion on the threads.

Run the nut down on the stud and keep a box wrench on the nut.
Install a second nut on the stud and jam them tight.
Use the extra leverage of an extension (pipe or second wrench) attached to the wrench on lower nut to break the stud free.

A quick sharp tug usually works.

Apply heat to the stud, or get a longer pipe, if the stud is still stubborn.

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78 W116 300SD 'Desert Rose' new as of 01/26/2014
79 W116 300SD 'Stormcloud' RIP 04/11/2022