When I went to put the snow tires on my car over the weekend I noticed the valve stems had serious dry rot type cracks in them! This could easily result in a tire blowout.
I believe these have only been in the wheels for 1 year, and only used during the Winter. I store them in a cool corner of the garage for the Summer, so really they only have about 6 months use which is amazing. Since I have a tire machine, I personally mounted the snow tires on the rims, and changed the valve stems when I put the tires on. Typically I try to use steel valve stems to avoid rubber defects, but these particular rims could not accommodate the steel valve stems. It is the first time I had an issue with a rubber valve stem, but reaffirms my belief in metal valve stems, and the need to change them frequently and check them often!