Thanks for the input, everyone. The 2007 Hyundai Elantra is one of those cars with a normal-use maintenance schedule that just specifies inspecting the fluid every 15K miles and replacing it at 105K miles (with no explicit mention of the filter). Then again, the maintenance schedule ends at 150K...
I don't have any deep knowledge of ATF's, transmissions and the like... just looking for a cheap / convenient source of some equivalent to Hyundai SP3 for a 2007 Elantra GLS at 240K. (The fluid cooling hoses are accessible, so it's easy enough to do a flush, last done at 120K with Valvoline...