I had my WRX flushed and filled with Redline Hi-Temp ATF today. after 42,000 miles of abuse, my factory fluid was pretty much fried. shifting was hard, wierd from 1st to 2nd, and the tranny felt laggy off the line. after flushing it and filling it with the redline stuff, it's all better and even feels much better than stock. shifting is silky smooth, firm, and fast. the transmission feels like it engages much better from a standing start. according to redlines site, this stuff can withstand a lot more heat without starting to loose performance.

the downsides? it's expensive. $8 a quart, times 10 quarts to fill up is $80, but it actually costs more than that. the place that did mine used a Wynn's flushing machine which needs 14 quarts to do it's thang. sounds wierd, but the process ends up loosing 4 quarts due to interaction with the old fluid. so, 14 quarts @ $8 plus about $70 in labor is one hell of an expensive tranny service. but, it's worth every penny. this is about as much as you can do to the tranny without physically removing it from the car.

 

It has to use 4 extra quarts becuase it needs to flush out the torque converter which would have still been filled.

I think its like 75% of fluid drained with just dump and pour and 95+% for the machine.

 

it's actually less than 75% drained. it's about three quarts.