There's a whole academic discipline to conservation that considers
these issues, but essentially a museum needs to think what it wants
to achieve and then decide how to go about making it happen.  Long term
academic preservation or present-day entertainment?  Maintain original
fabric or replace?  Revert to original condition (including undoing
modifications) or preserve as received?  There's no single right answer.

Those who know just how good these machines can be clearly want to
restore to "as new", so all can share the joy of the original
perfection.  That's fine, but it maybe over-estimates the original
customers' experience -- I'm sure that if transported back in time to
the old West you would find that many (most?) commercially-operated
instruments there didn't play perfectly, or were indifferently in tune,
quite a lot of the time.

To many folks that "not quite" quality is and always has been one of
the hallmarks of mechanical music, whether we like it or not.  Should
a museum keep folks happy by pandering (if only a little) to their low
expectations?  Informed enthusiasts would be horrified but for an
entertainment-oriented collection it might not be entirely inappropriate.
Think of all those out-of-tune "tonkanolas" that have been recorded
over the years.

To me, an important and often-ignored aspect of the hobby is how
perceptions of instruments have changed with time.  What we see as
collectable instruments were actually made as profit-generating
commercial devices to be discarded when something more profitable
appeared on the market, and all surviving instruments will have a story
of continual decay, disposal, rescue and repair that should be told.

The issue that started this, the Montana collection's retention of
fairly crass 1970s labelling of "obnoxious" machines, suggests a rather
muddled conservation solution.  I'd incline to displaying the 1970s
labels separately as part of an exhibit about the machine's history,
because such labelling illustrates an intermediate point in the
machine's life, roughly the point when it had been rescued but prior
to its qualities being fully appreciated.  You clearly don't want to
keep such a label on a restored machine because the label (one would
hope) doesn't apply to it in that state.

Julian Dyer