Here is the airflex website. air-flexx valve extensions - top notch technology for the toughest environments
. If you search around you will find some interesting information regarding tie down, and what is the proper valve stem rubber or metal, to attach to on the inner and outer rear wheels.
One issue I see is during the recommended MB tire rotation described in the maint section, you will run into a conflict because only one of the rear wheels has a metal valve stem, while the other is rubber. That will not allow you to do the recommended rotation of the wheels, per MB, because Air-flexx has specific requirements on which rear wheel valve stem must be metal and which can be rubber. Not sure who set up the rear wheel set with stems, but there would be a conflict upon rotation of the tires as recommended.by MB.