Front End A Shakin' (Warped Rotors?)

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Two years ago I replaced the rotors (all four) and was quite happy with
the results.  They were not cross-drilled, enlarged or otherwise, but
were stock.

Two years later when I lay on the brakes relatively hard, the front end
shakes considerably.  It is more noticeable when you have really laid on
them, and you are in the very end of a long and hard stop.  The shaking
comes right up through the steering wheel, and several passengers have
remarked of this.

Questions:
1. If I sell the car this fall (most likely dealer trade), can it be let
alone through the summer without killing me?
2. It is warped rotors, as I have heard?
3. What caused it?

Thanks-

Todd
fOrMeR qCuSa #356
'90 80Q