At a glance
What can fail
On certain vehicles, lug nuts can bottom out on the stud shoulder in single rear wheel setups, reducing the clamping force that holds the wheel to the axle. This could cause a rear wheel to separate while driving.
What the fix does
The rear wheel studs will be replaced with revised studs designed to prevent the lug nuts from bottoming out.
Summarized — see the official notice for exact wording, dates, and contacts.