Another possibility is to simply rerun the
combo installer for the version of the OS that you currently have installed.
This should replace any files that are necessary.
thanks both for your suggestions. I had already been through PRAM zap and preference farming per suggestions on another thread re. bluetooth decay.
Further to above, threads suggested limited reinstall using pacifist - and while that may work for some sections of the OS, bluetooth seems to sprawl through many different areas of the disk making it far from straightforward.
So, rather than cause more damage and headaches, I did a full reinstall and archive a few days ago. Pita for apps, but Bluetooth came back smiling, as expected.
One piece of advice to others in similar predicament: don't assume it's a hardware problem if/when BT disappears. System profiler can be a useful tool in this situation on several levels.