I picked up an insert from Bruce last week that contained a really ugly snipe. Didn't pay much, so I was willing to experiment some.
After receiving the poster, I took a look at the snipe. It was partially peeling, and the glue looked to be water soluable. Either wheat paste or something similar. It was definitely dried and cracking. I carefully worked the edges, getting the glue to flake off and slowly removing the snipe. This took off about 75% f the snipe with no effort. I then tested a corner with a damp sponge, and was rewarded by the glue becoming gummy and coming off. I then used the sponge to soften the snipe and slowly got it to separate from the glue and come off. The whole process so far took about 45 minutes. As I suspected, removing the snipe revealed that this was a roadshow #D release poster that had been repurposed. So here is where I am currently sitting. The glue is slowly coming off, but whoever put it on was sloppy, and there are runs of old glue. Further, it was slapped on and then the snipe shrank, causing the upper edge of the poster to ripple. Here is where it currently sits:
Obviously a lot of work left and it likely won't ever be better than good on a Bruce scale. I have some tricks from my old photo studio days I am going to try, and also work on getting the rest of the glue marks off. Will keep you posted.