Are you breaking old ones (pulled from junkyards), or are you referring to something "new" (like the Dorman "Help!" line at Napa)? How are the crank handles actually failing (the part that turns the regulator strips, the knob falls off, the handle itself shears between the knob and the regulator connection, or something else?
My XJ's a 92 and doesn't have crank windows, so don't know how that part attaches in a 97+.
Have you