just go with another trans
$500 is a start
by the time u pin point which ones cooked
ur already wasted same or more money as a new trans and wasted about x 6 more time and ATF (which is not cheap)
if your thinking your gonna get away with $500 your gonna be in for a good ride
iv been doing these trans for years
people who dont wanna spend the initial money (Service or just replacing 1 part ) always end up spending more