[Shotimes] Front Rotor Warping

[Jim and Debbie Leyden]

A little over a year ago I upgraded my brakes to the 11.6 front rotors.
When I did the conversion I used new pads, rotors, brackets, slider pins,
calipers and backing plates.  The knuckles were purchased from a boneyard.
About six months ago the car started to vibrate when braking.  I checked the
front rotors and found that there were casting porosities in them.  I talked
to the place where I purchased them and they agreed to credit me the cost
towards a set of PowerSlot rotors.  Well, now six months later I again have
a nasty vibration from the front end when braking.  My wife and I have been
VERY careful with these brakes so as to not overheat them. (I DO drive
rather hard but I use engine braking as well as brakes)  I talked to the
shop where I purchased them and was told that the same situation had arisen
with the owners car (powerslots also) and he merely had to take them out and
REALLY heat them up to correct the problem.  I tried this, it seemed to work
for a little while (couple weeks they were fine) but now the shaking is back
and even worse then before.

Any clues as to why I can't keep a set of rotors from warping?

Jim
'93 MTX
perfect for that commercial where the guy is shaking his chocolate milk.