I think you'll get a lot of response on this, but I have one idea
that might be different...
First, you cannot fix it without taking out the turquoise. Really.
If I understood right, and the joint is on the back of the setting,
water will not help.
It may be easier to take out the stone than you think. If it is a
fairly normal bezel, it is generally possible to insert a thin steel
tool between the stone and the silver and very carefully, slowly
coax the silver away from the stone. My favorite tool for this is a
dental-type tool with a profile sort of like a golf putter, but very
flat. In other words, it is a tiny spatula that sits at an angle to
the handle. I bought a very nice set of such tools at Blick Art
Supplies. I can't find the exact one online, but these are the type,
and one of these might work: http://www.dickblick.com/zz330/77/
The idea is, you need a smooth hard steel tool with a somewhat sharp
edge but very strong and not too sharp, so an exacto blade, for
example, is a poor choice-- it is too sharp, too flexible, and
breaks too easily. You want a teensy butterknife, in effect, so you
can slide it along between the stone and the bezel.
Usually, bezels opened in this way can be annealed and put back,
really none the worse.
Worst case scenario, you have to choose between saving the stone or
the ring. Can you choose wisely? And if it makes you feel any
batter-- we've all done it.