VW,
The cap screws down and around the bolt assembly. I Googled the term you used and found a picture of a FSA 'top cap' similar to mine. Earlier attempts were for naught.
From the web: "These Top Caps are specifically designed to minimize damage to forks with carbon steer tubes, as a safer alternative to star-flanged nuts. Compatible with 1 1/8" carbon steer tubes. Includes top cap, adjuster bolt and expander. Weight 34grams. "
It scares me too that my LBS can't seem to solve the problem. I bought the '05 bike at a spring warehouse sale earlier this year for a really great price. The LBS is a is a chain of 5 family owned stores and not a by any stretch a big box store. Bikes are but one part of their product line. Hmmmm.
My enthusiam for cycling is not, unfortunately matched by my knowledge of the inner workings of modern bikes. I suppose I'll go to my LBS that sold me my Trek two years ago. Their service is probably the best in the city. $$?