OK... Let's take a different tack: Have you logged in to a test user account to see whether your issue follows you across account lines?
Edit: Another thought... There are apps that get deeper into your system's caches than Cocktail does, and it may pay you to try one of them.
I suggest
TinkerTool System...shareware that allows you to do some experimentation before buying; run it's entire cache clearing suite in one shot, and see if it helps.