John Charles said:
But--Slayton's recollections aside--does anyone really believe that
any of the astronauts played an absolutely indispensible role in
making Skylab--or Apollo, or Gemini, or Mercury--flyable?

Seriously, I am asking for evidence of any astronaut's contribution
that was superior to lots and lots of non-astronauts, other than the
word of another astronaut.

That's an awfully difficult question to answer. In my own profession,
I've learned that sometimes the best thing to do is ask a difficult
question and let someone else deal with the implications. This avoids
the need to say "you are wrong", and it lets the other guy say "that's
interesting ... you know, if you take that idea and combine it with my
idea ... then you think about....". A single carefully chosen question
can guide someone into thinking deeper about a problem, and devising a
new solution, without the ego-issues of saying "you are wrong, I'm
right".

Mike Collins hints that he did this as a test pilot in Carrying The
Fire.

Wally's "I'm cooler than you, let's light this candle" might be an
example of this.

There is a classic example of this in From the Earth to the Moon where
Armstrong is in the LM simulator and just says almost nothing during a
simulated landing. The descent rate it too high and the simulated LM
crashes. By saying nothing, Armstrong manges to get Mission Control to
think about what they are doing and resolve some incorrect attitudes.

Wasn't there an Assimov story that dealt with the least possible change
to create a desired effect? There is an almost occidental philosophy in
saying almost nothing to generate the desired effect. If we assume the
astronauts were bright, they could have done this in a way that hid
their contributions.
--
Kevin Willoughby lid

We'd spend the remaining time trying to fix the engine.
-- Neil Armstron