I had previously scraped, rinsed and dried for several days before introducing alcohol.
It's common for some substances to be alcohol soluble and not water soluble. The alcohol still could have dissolved tars that water had no effect upon.
Actually, alcohol is less well absorbed by wood than water. That's why the ABV of whiskey rises when stored in oak barrels. The water evaporates through the wood, but the alcohol does not, or at least at a significantly slower pace.
If anything would have caused swelling and cracking, I would be apt to point to the water.
Just a theory.
By the way, in light of the crack, waterglass might be a more appropriate fix than pipe mud. A crack can allow in air, heating up the wood around the crack, resulting in a burnout. Waterglass could actually seal the crack.
@georged created a video where he talks about applying it.