My window sill is warped, but that's not the problem.  The problem is
that I can't remove it to replace it.  The window is a ~ 6'x6' picture
window, double-paned and probably < 10 years old.  Not original to the
opening of the house built in 1947.  The interior ?frame? is
essentially a square box built around the edges of the window after it
was installed.  The wood on all edges probably only extends over the
glass < 1 inch.  I assume there is metal edging the glass, and I don't
know how wide that edging is.  The bottom sill, starting to rot and
already very warped by the moisture, was screwed down into the wall
with 4 screws.  I took those out, the sill is now loose along all axes
I can move it, but it only wiggles.  It should pull out horizontally
from what I can tell, but I can't get it to move even a fraction, as
if there were additional hidden anchors keeping it from sliding out. 
In search of these hidden anchors I removed the screws holding one of
the sides sills in place.  The sides sit on the bottom sill.  I wasn't
worried about damaging it since it was poorly placed with a big gap
just squirted full of insulating foam, and is also starting to warp. 
I figured just to replace it too.  But even with the screws removed,
and the foam and plaster bonding it to the wall removed, I can't move
that side sill.  As I try to pry it I can tell it is firmly and
generously glued to the window pane.  At this point I don't know what
to do.  I tried all the tapping and prying I thought I could safely do
without damaging the window.  I tried to use a utility knife to cut
between the wood and the glass.  The glue bond is so tight the knife
would rather cut into the wood, but patiently and carefully I cut into
the gap as deeply and thoroughly as I could.  It seems to make no
difference.  If the metal edging of the window is as wide as the wood,
it could still have > 1? of surface mated to the wood along its
length.  And that's assuming I cut as much as I could with the knife. 
I can tell the bottom sill isn't attached to the glass, but I have
every reason to assume the top and other side are glued as well.  And
I can tell from the movement of the glass when I try to pry the side
sill that the molding on the front face of the glass is glued to it as
well.  I haven't considered using a solvent yet because I'm afraid of
damaging the seal of the double-paned glass.  Same worry with too much
prying and tapping trying to break off the glued wood.  The thought of
removing the whole window with glued-on sills attached crossed my
mind, but even then would there be a way to separate the rotting and
warped wood?  What are the tricks the experts use when they come
across such and ill planned and seemingly irreparable construction? 
I'm fairly handy.  The glass itself seems wonderful, and at its size
I'd much rather put the effort into repairing my window than the money
into replacing it.  I have photos if you are interested.  Please help.
 Thanks, Joel Barnes