Did a search, didn't find anything, so - recently we received a safety notification from Ford advising us to check the valve stems on our '07 vehicles. Seems they're developing cracks, allowing the air to leak out. Some info.
Happened on my '07 Expedition.
If they can't get us with lead in kids' toys, they'll do it with melamine or defective drywall; whoever is left will get wiped out by faulty valve stems...
The commonly available valve cores for Schrader valves are also of bad quality. Ever since I replaced the valve cores on all my car and bike tires with a good brand, I have had to add more air much less often.