I own a 2001 Elantra and it would have problems shifting.
So, I drained the ATF and put new ATF in.
I think it has to be SPIII compatible,
Well, so far the transmission is still working.
Oh, when I first bought the car, it would shift hard from park to drive if it was cold outside.
Brought it to AAMCO and $400 dollars later, it was fixed.
I just don't know enough about transmissions