My condolences.... Many shops won't work on Ov*tions because they are a huge can of worms in terms of lousy construction, lots of use of ep*xy, etc. and a penchant for developing permanent dimensional instability in what little wood they have....
Nonetheless you're being a good guy and helping someone out and that always motivates me to help too!
Notice how thick the finish is........? Have a little guitar with your finish eh...
One of the Luthiers at Elderly instruments developed a technique for difficult cracks that either won't close or if we can force them closed we are likely to cause additional cracks somewhere else. We've used this technique a number of times with great success AND only when appropriate for the instrument. It's not something that I would do with a valuable or vintage valuable instrument but with an Ov*tion and when no one's looking it just might help get you and your friend of a friend where you want to go.
Cleat the crack open instead of attempting to close it. Something in the order of back joint reinforcement spanning the crack with appropriate grain direction is how we cleat the crack for this method. You will see why in a minute. You are also creating a "floor" for glue application.
I heard you about the fan braces, yet another reason why many shops won't work on Ov*tions in so much as traditional techniques don't apply well with these.
Once you figure out how to cleat the crack open with a full length cross crack strip and integrate it to the existing fan brace(s) you are ready to seal the crack.
You can mix up some quality structural ep*xy such as West Systems, System III, or even Bob Smith but use long open time of at least an hour mix the epoxy and yes you can color it with trans tint dye.
With nitrile gloves on and some ventilation apply the color matched ep*xy to the crack and smooth it all out. Use only water to clean, carefully.... ep*xy off areas where you don't want it.
Let cure a couple of days and then level sand and buff, bill the client, next....
As mentioned this is not a method for a 1936 Martin OO-18 or any other decent instrument but for an Ov*tion who cares..... This is the "appropriate for the instrument" thing.
Be advised that this kind of crack is often also a tell tale of other RH related issues, lifting bridge, etc. And Ov*tions are not immune from needing neck resets as well.
As such if there is no way out of this one.....
and you have to fix the thing this method would work fine for what you have.Consider the idea as well that we could force this crack closed but in my experience if once rehumidified the crack will not stay closed on it's own at 45% RH you will likely develop more cracks as a result of adding stresses from closing this one. That's when filling is advisable over closing.
Hope this helps.
