I bought an FS-4 starter today. Things started looking good when I removed the glow bulb from the can and it looked to be the same dimensions as the faulty glow bulb I originally removed. I soldered the FS-4 in place and the fixture works perfectly.
Thanks to all who made constructive suggestions for pinpointing the problem and for suggesting the fix. For whatever reason, the 18W lamp bulb seems to require a starter normally rated for 30/40W bulbs.
It was worth the time and effort. Cost me $2 in parts (1 failed attempt with the FS-2, and the successful attempt with the FS-4) and about $2 in gasoline to salvage a lamp that I would have had to spend at least $70 to replace.