I've been using the 85* steel stems from Kurveygirl since my first tire change. Bike now has 57k miles. I replaced them the last time I did tires, because I noticed some cracking on the outside of the outer sealing grommet. When I actually took them off, though, I inspected the seals and found that I shouldn't have worried. It was only the very outer surface that had any cracks. The seals were very good shape. But I figure with about 40k on a set, it was cheap insurance to replace them.
http://kurveygirl.com/shop/product_info.php?cPath=27&products_id=72