Crank bolt to hold damper

Fine threads see less strain than coarse ones so are less likely to pull out.

This bolt sees a pretty huge level of clamping force with the 135 ft lbs of torque, which is necessary to lock the damper hub to the crank, so that the hub is essentially part of the crank. That is necessary to couple the internal, torsional crank vibration energy into the damper. If the bolt is not torqued down properly, it is possible for the vibration energy to be concentrate partly in the threads rather than traveling through them to the damper hub, and that will eventually worry them out. And if fewer threads were left the last time that just concentrated more force on the remaining threads and made things worse. So that may be what has happened.

And no way I would helicoil it for these reasons; just another improper place for vibration energy to concentrate and cause future failures. Similarly, any locking compounds substituted are doomed to fail IMHO; I seriously doubt that they are intended to survive for long with the levels of vibration energy that can flow to the damper.

So any cure that does not allow you to get to the full torque on the damper bolt is cause for future failure. So I personally would move right to tapping a new hole but of minimal size increase. That is because the thinner the material that is left in the crank snout wall, the more vibrational strain it will see. For the reasons above, I personally would NOT recess the start of the threads in to the snout but start them as soon as possible. The advice to put in a recess is good for keeping them straight, but I would employ another method for starting straight threads rather than losing material anywhere.