I am sorry to be late to the party, as I had not been monitoring "Page Two" of my own damn forum, because I thought Page One indicated no new posts (that issue has now been addressed!)
Don't worry about the crack in NU67 rectifiers. They all have it, more or less, and all work just fine.
As to suddenly no juice from an otherwise healthy looking and functioning NU67:
The power switch can get intermittent through the years, and sometimes does not make proper connection between stationary and moving contact points.
I have more than once took the switch apart, cleaned its contacts from oxidization and lubricated it before reassembly. Everything will work fine again.
An interim solution: unplug the supply form the wall, and activate the power switch 20 times.