Is it the glue, or is it the binding itself?
I’d try a little naphtha first, then the sand and buff.
The binding glue is smeared on the finish and looks to be 'flashed' into it. Water and naphtha won't dissolve it.
Then I’d go to the sandpaper and buffer.
Paul makes a good point. Through my color neglected laptop monitor the binding looks very white. Maybe someone did take a stab at repairing that gap. I've heard its really easy to take something bad and make it much worse. In fact I think someone was referring to me.
Unless the contamination can be taken off mechanically and there is original finish underneath it (a lot to ask for), this looks like it wants spot finishing.
This won't be ready in a week or ten days.
Hard to tell from the photo, but is that wood glue? If so, I'd recommend lightly brushing some vinegar on, letting it sit, and then seeing if the glue comes off after an hour or so. This way, you won't have to disturb the finish. If not, then yeah, wet sand and buff, and hope it hasn't eaten too deeply into the finish.
Looks like you're going to need to re-do this repair though. White glue isn't the best choice for gluing plastic binding, and Martin's tend to have binding shrinkage in the waist anyways, so I'm not too surprised to see it pulling away again, if that is in fact white glue.
My bet is that it’s acetone based binding glue.
Thanks all, I've been away for a while. I think this is above my pay grade, so I won't mess with it. I'll send it off to a friend who does top-notch finish work. Hoping for the best. Tom
There is a lot of binding cement. First thing I would do is scrape as much off as possible, I doubt it’s stuck that hard to the guitar finish. Then you could wet sand with wet and dry sandpaper, starting with 800 grit and up tp 2000 then buff and polish.
looks like there may be gaps in the layered binding that will also need redoing or replacing.