As promised, a description of the 78's starting difficulties:

I put the key in the ignition, turn it to ON, the two red lights come
on, then I turn in to START.  Chunk.  That's all, doesn't turn over.
Turn it off, then back to ON.  Nothing at all, not even the two red
lights.  Hit START again, not even a chunk this time.

Dead battery, I thought.  Something drained the battery down
overnight.  So I played around with starting it from my other car's
battery.  In the process, I learned that a) that didn't help, and b)
the bus's battery is holding a nice steady 12.8 V.  Okay, maybe the
battery's not dead.

So I try starting it from its own battery again.  It cranks over this
time, but won't start.  Hmmm.  Try again.  Nothing.  No lights on the
dash, in fact, the door's open this time, and after hitting START, the
door buzzer is not even buzzing.  Check the clock, the clock is not
ticking off seconds.  Dead stopped.  OK, apparently not the ignition
switch.

After each attempt at starting, the whole electrical system--fused,
unfused, switched, unswitched, everything--just shuts down for about
30 seconds.  Nothing I do in that time produces any result.  I tried
measuring the voltage across the battery during one of these outages,
and THAT didn't even produce a result.  My DMM reported
"OL"--overload--which would normally indicate a voltage out of its
range, i.e., greater than 400V DC.  If there was a dead short
somewhere (like through the starter), I would *think* it should read
zero or close to it.

I also thought that the single "chunk" might indicate that the starter
gear is sticking, and tried Muir's approach of putting it in 3rd gear
and pushing it backwards to unlock it.  That didn't help.

After playing with it for an hour and experiencing about 6-7 of these
outages (and of course the one time it did crank), the battery voltage
was down to about 12.4V, and I decided to give up and mull it over and
seek opinions.

Any of this ring a bell with anyone?  Like I said before, I'm gonna
run through as many of Muir's procedures as seem applicable, and if
that doesn't help, I'll report back... but I'm open to suggestions.

-Rodney