I've heard from many mechanics that the Elantra's of this generation have fragile transmissions. If the fluid isn't frequently serviced, one could have issues. Even with maintenance, it's the luck of the draw. I have an 05 Elantra with 80k miles on the clock. The trans. is still good despite only one fluid change at 50k miles but who knows what the future has in store.
they are not fragile. people do not pay attention with the fluids that the transmission requires. either OEM hyundai, or vavoline maxlife are usable for XD, XD2, spectra's, etc.
also the speed sensors tend to go out after awhile, but that is a-typical for most vehicles.