Mark567 wrote: ↑
Wed Jan 02, 2019 1:31 am
On the 1st string 8th fret, 2nd string 13th fret, and the 3rd string at the 26th fret they ring for maybe one second or so then die.
26th fret? How about 3rd string 17th fret (standard tuning)? They would then be all at the same frequency, 523.3Hz. In which case it would be a coincident body resonance at that frequency causing the problem. The fix is to find the shape of the top's mode of vibration at that frequency (using Chladni patterns) and mass load the antinodes to change the frequency, whilst not shifting the frequency of other modes that matter. It's a simple fix once you know how to do it and have the gear to visualize the offending mode of vibration.
If the above means nothing to you, you are unlikely to have the equipment necessary to do the work yourself, in which case you will need to find a luthier who does understand this stuff. Unfortunately, there aren't too many of them about. It's not in the "tool kit" of your typical guitar tech.