Thanks for the tip, but been there, done that.  :)

In addition to the lower mileage, last Fall I started to have harder
starting and rough idling problems.   In the process of changing the
fuel filters, after using the priming pump, that developed a leak, so
I replaced it.

The fuel filter problem was the strangest thing I've seen.   The only
symptoms were harder than normal starting and then rough idling.   It
got to the point that it was shaking and almost stalling when stopped
at a light, yet would do 70 down the highway with no problems.    I
can only guess that somehow with a clogged filter the fuel pump at
ideal may not have been capable of delivering fuel, but at higher RPM
it could?    I could also rule out the leaking primer pump as the
cause, because it wasn't leaking that badly so I was able to drive it
with the new filters with the old primer pump and the idle problem was
totally gone.

Anyway, pretty sure now there are no fuel leaks.   No spots on the
garage floor, no diesel smell.  Also, the usual suspect fuel line
return hoses are not leaking either.

I was going to take a look at an area in the driveway during the next
light rain with the car running too, just as a final check.   But, I'm
probably going to replace the injectors, as that would seem to be the
next logical step.  The car has 125K with the originals.