I had a good experience with an aftermarket part, so I'll share it.
The part is the window regulator, right front passenger's window. It's a nasty piece of kit, a design that's probably being used in most cars nowadays. It consists of an endless-loop cable that pushes/pulls the window up and down. The motor bolts onto the regulator assembly. The array is sort-of like a triangle. Two legs are the flexible cable/shroud that's bendable, allowing you to awkwardly manhandle it through the available openings in the door. The third triangle leg is rigid: it's the steel track that guides the nylon "foot" that holds the window glass. The motor goes at the apex where the two flexible legs join. You re-use your old motor.
These regulators are very specific, custom for each car by car model, left or right side, which window, and whether it's power or manual. In the case of my Sonata, the same parts were used for a run of a few years.
It's necessary to maintain tension against the cable at all times. If tension is released, even for a fraction of a second, the cable jumps one of its two pulleys (either rollers or slides) and instantly kinks or knots. When this happens, you have to replace the whole assembly. In order to prevent the cable from jumping, the track is "lubricated" with what looks like a special sticky silicone paste. It's actually a movement retardant. For the original assembly, Hyundai published a routine for repairing the slider/pulley with a different part.
It's a real Mickey Mouse design, and as I said, it appears that, like being surveilled on the internet, "they're all doing it" (which is not true about the internet - but then there's Google!).
My driver's window mechanism broke maybe 4 years ago. I bought the part from the dealer, around $58. It appears that there had been a lot of failures of the originals because the replacement appeared to be an improvement. My friend had the identical tangled cable in his GM car. His part cost around $150.
In my case, the cause of the failure was obvious: I hit a very nasty, sharp, un-marked speed bump. The sudden shock caused the window cable to jump the track, audible the next time that I lowered the window. (Stay off side streets in San Pablo, California.)
For me, my friend ordered an aftermarket regulator made by Dorman. $38 complete with delivery. I was pleasantly surprised. The part seems well-made. Fit was accurate. Embedded bolts were protected with plastic thingies for shipping.
What is especially impressive are the extended custom nylon shrouds at the ends of the track, where the cable turns a sharp bend, one shroud at each end of the track. These are the points where the cable jumps off and kinks. Dorman took special, intelligent care to guard against cable jumping at these two points. My only complaint is minor: the window doesn't retract completely; about 1/4 inch sticks up above the rubber gaskets. Movement is smooth. In all, I think that this part is actually better than Hyundai's original. Frankly, I think that Hyundai should buy these parts from Dorman. I'm pleased. Of course, time will tell.
Someone recently noted that his Dorman drive train part failed prematurely, so my good experience may not hold across different types of their products.