Closest glue I have seen to that is Pratley Pliobond, which is basically synthetic rubber, chalk and solvent in a tube. Thus the rubber degrades with heat and time after exposure to atmospheric oxygen, the filler chalk often is the lowest grade contaminated reject powder, which is bargain basement price because it is either contaminated with heavy metal, leachate from a mine runoff, cyanide or other organic chemicals or is simply a reground recycled concrete blend. Solvent is whatever would dissolve the rubber so could be almost anything or a blend of whatever.
Thus the glue will with time both decompose as the rubber dies, and the moisture in the air will be attracted to the filler and wash out the soluble ions there to corrode the board.
I guess they did a dab of glue to fix the caps, and the person doing the application rested the glue gun on the board while doing something, leading to the drop on the crystal. As well probably the original spec called for a certain manufacturers part and this was substituted by the assembler as the original spec was either expensive or they had a stock of the cheap junk already, used on the simple SRBP TV boards and PSU boards they normally make for others. There a slightly corrosive glue is not a worry on a single sided board with no voltage across the glue and only plastic sleeve and anodised aluminium oxide capacitors there.