Kevin, I have restored three 125's, so perhaps I can help.

As this failure was sudden, I would start with taking a reading on the
amount of suction.  These little organs take a lot, and the suction
pump is almost too small to do the job.

Because the problem was sudden, the first thing I would look for is
suction pump trouble and also the attached reservoir.  The reservoir is
an easy check.  You can see whether it is almost closed, about half
open, or almost wide open.  About the only thing that can be wrong
here, if the vacuum pump is working properly, is the spill on the
reservoir.  It depends on suction to hold it closed.  If there is
something preventing this from closing--a bug, some little bit of junk--
a lot of suction can be lost.  Also, has the stick that makes this
spill open, moved or changed dimension due to temperature and humidity?
Of course, the cloth could have started to fail, and it is just leaking
badly.

With the organ in PLAY, but the roll stopped, watch the reservoir
carefully.  It should remain somewhat steady.  But if there is a
noticeable drop that repeats itself in a steady pattern, you can bet
there is a bad section in the pump.

The main cause of that is that the interior or exterior flap valve on
one section of the pump is not working.  Some of these had very tiny
springs attached to the leather flap, and after years of work plus
corrosion, one of these could have failed, so that suddenly you have
lost 25% of the suction produced.

The suction pump on a 125 is not easy to get out.  There are ways to
test each section of the pump without a lot of dismantling.  Go in
through the service panel that gives access to the pump drive sticks,
and slip the sticks off the wrist pins.  Now you can manually operate
the pump bellows by hand and can quite quickly, by being able to
isolate each quarter of the pump, find the section that is not doing
its job.  The use of a gauge takes the guess work out of this.

By this manual test, if all four sections of the pump are producing
equal work, then at least you did not have to go through all the work
of pulling the entire pump out through the top of the case.

If none of the above have shown to be a problem, there are two more
things to check.  Look at the stack and the push rods.  Is there a lot
of lost motion?  I have seen these stacks tilt forward due to a
mounting screw failing.  Also I have seen them warp enough to not play
the center sections.  

Lastly, check the cut-out valve that controls suction to the stack.  It
is possible that the large pouch inside this valve block is not
operating properly, due to a leak in the signal tube that comes from
the transmission area.  The original tube was made of lead and placed
in just the right spot to be hit,  damaged, squeezed shut, or its
connection (made with burnt shellac) to a wood pallet valve broken.
Again, an easy test to isolate the trouble.

Good luck with the Ampico.  There is nothing finer when they are
playing properly, not even a Yamaha Disklavier.

If I can answer any more questions, just ask.

Ken Vinen
Aylmer, Ontario, Canada