Re: my guitar's paint is cracking - WTF?
In the future, if you have a nitro finish, you can re-amalgamate the lacquer with a solvent like Behlen's Qualalac or Blush Eraser. The active ingredient is Cellosolve which is a direct solvent for nitrocellulose. Cellosolve allows the cracked nitro to become liquid and re-amalgamate into the other nitro layers. Since nitrocellulose lacquer melts into each other, this is a great way to stop checking in it's tracks.
Just use enough amalgamate to get it going, but not so much that you cause the nitro to shift or run.
Cellosolve is also an instant brain killer and known carcinogen, so use it outdoors and wear a repirator when applying it.