That type of damage is typically caused by overheating which can be the result of any of the following or in combination:

1. clipping an amp into the speaker
2. if the series capacitor, C2 was too large or shorted
3. if the parallel resistor, R6 is open.

Thanks for getting back to me. It's very helpful to know which components are most likely to be causing the issue, because I don't want to desolder any that I don't have to and risk applying excess heat to them. All of the capacitors are 15μF to match the originals. I just want to check - did you mean to say series capacitor C3? Because C2 appears to be in series with the filler rather than the tweeter. I will check R6 after the capacitor, because no heat was applied to it in the soldering process so I think it is less likely to be the issue.