1N4742 is a 12v zener diode !
Can you test these diodes with multi meter ?
If your meter has a diode check function even better.
I will bett one or more is faulty,
this would explain the demise of the
current limiting resistor.
hmmm... all 5 failed the same way? That = poor design for the fixture circuit itself. Probably a Chinese knockoff. If you really want to go on the cheap you can replace the resistor and go with CFL floods, but I'd be scared to death to try that and instead would bite the bullet and purchase quality fixtures. You just can't overplay your family's safety here. What if one of those caught on fire while everybody was asleep?