Jeffrey said:
"Sure, but the first thing that happens when you
RELEASE the button is that the gears ENgage, and I
suspect that's when they break."

Unlike the tranny gears you mentioned, these gears rotate very
slowly and weigh a fraction of an ounce, and meet little resistance
to turning.  I don't think they are capable of generating enough force
to do any damage, but it is still a valid observation.

I DO agree with you, though, that if you press the button gingerly,
and only at full stop, you can make a fragile odo last a few more
months or even years before it eventually breaks.

Best thing to do is take the speedo unit out, lube everything, and
put a gob of epoxy in behind the tiny plastic ring that holds the
axle in place, and thus avoid having it break.  Preemptive strike!!!
Then you don't have to worry about it anymore.  :-)

Bill Marshall
85 GL Tiico "Pandora's Box"
Aurora, IL