+1 to the previous comments.
All too often, people buy a used car that did not come with maintenance records, and wind up buying a vehicle that has seen little or no maintenance. Or, some folks might buy a new car and then proceed to ignore vital maintenance. The end result is the same in both cases, namely a drastically-shortened life span and/or high repair costs for the vehicle. And then, to make matters worse, many of these negligent people automatically assume that the problem lies with the automotive manufacturer, rather than with themselves!
Think of it like human longevity. As the availability of vaccines, life-saving medicines, and advanced surgical techniques have improved, so has the average life span. However, if someone smokes, is a couch potato, and fails to seek medical treatment, he may wind up living only as long as folks from earlier in the century.
Ergo--with your car, and with your own body, it is necessary to periodically take steps to ensure long-term well-being. This particular Elantra has not been maintained properly, and the OP is now paying the price (literally) for that lax maintenance.