Doug, I had the same experience with some Vittoria tubulars that were in storage. The bond between the brass stem and the tube failed. I fixed them by taking some old patched presta clincher tubes, and cutting out the stem areas, leaving the thickened portion where the stem was bonded still attached. When you look at them from the inside, you can see how the stem and a tapered section of rubber are bonded together, and then vulcanized to the tube. Using a sanding belt or disc, carefully buff away the tube from the portion bonded to the stem until you have just the stem and about a 1/2" x 3/4" oval of rubber that tapers to a very thin edge. On the tubulars, peel back the base tape from the stem, and you will notice that there is a different type of stitching for about 1" on each side of the stem, as this is where they do the final stitching to complete the tire. This is also the easiest area to restitch. Cut the different style stitches, and pull out a loop of tube to allow you to work on the stem area of the tube. Pull the original stem out of the rubber the rest of the way, and then carefully buff away the raised area where the tube was bonded to the stem/base. Make sure you have a flat buffed area a little larger than the stem and base you prepared, and then glue it on with self-vulcanizing cement on both surfaces and clamp it until dry. Be careful not to get any glue inside the tube, or in the stem hole. Stuff it back in the casing, sew it up, glue the base tape back, and you're good to go.
Davis Jensen
Lomita, CA