The most worrisome crack caused by moisture is a crack that goes through a tone hole. Passing through a tone hole will result in a leaking, unpredictable instrument. These cracks should be taken care of as quickly as possible. L&P offers tone-hole crack prevention, which almost entirely eliminates the possibility of tone-hole cracks.read more.
If you notice a crack through a tone hole You don't need to panic! Just follow the advice from the article
Tone hole replacement
A crack could open up again, anytime. Therefore, it is important to replace the broken wooden tone hole with a crack-free synthetical material like Delrin as soon as possible. The tone hole-pad connection will stay good, even if the crack opens up again. You might get a leak between the wood and the tone hole insert, but this can easily be fixed, even by yourself.(see article above.
To replace a tone hole is very safe! We have replaced thousands of tone holes over the years and it never changed the sound. tuning response.
Don´t get the instrument pinned under any circumstances!!! (Read also: Crack pinning )