Got a 2002 GC with the 3.8L ES package and tipping 90,000 miles.
All regular servicing and maintenance up to this point, though it does
need another throttle body cleaning and the serpentine belt is showing
wear.

Dealership gave it a thumbs-up on their 23-point inspection.

Then not 4-5 days later it began to sound strange when starting.
When the starter engages, it turns over fine and starts, but when
releasing the key (back to ON) there is a clunk noise.

My first guess is of course the starter assembly.
Possibly the bendix (sp?) if I remember the components correctly.

My question is how to diagnose it more finely before taking it to the
dealer?  I have extended car care, which is $100 deductible, if this is
the bendix, is that separate from a complete starter? Is it worth having
the dealer do and pay a $100 deductible, or is the cost so marginal I
should have an independant shop do it.

Alternatively, I have no fear about laying down under it for a couple of
hours, though I have large fingers - I could probably swap out the
starter myself.