To Change Your Transaxle Fluid (as posted on the Rennlist.com forums)

Very simple to change...in fact, easier than an oil change. The factory manual recommends this
action every 36,000 miles or 3 years and suggest you use SAE 80W API classification GL-4 gear lubricant. You will need about 3 quarts total. The gearbox will actually hold 2.75 quarts (2.6 liters). Most shops and seasoned owners will recommend that you use a slightly higher grade gear oil like Swepco or Mobil 1. The only tools needed for this job are a floor jack, four stands (or a lift), and a 17mm hex wrench or socket.

First, jack up the car level with all four tires off the ground. On the rear left side of the transaxle will be two 17mm hex bolts. The top is the fill and the bottom is the drain (duh!). Remove the drain plug to remove the old fluid. You might want to screen it to check for particles (pieces of your gears!) if you suspect a problem. I flushed some extra fluid out with air directed into the top hole. Then plug the bottom and add your new fluid to the top until the level is 6-8mm from the bottom of the hole. If you are buying your fluid by the gallon then you will need some sort of device to get the oil up there. If not, the regular gear oil 1 quart container will fit perfectly up there. When filled, replace the filler bolt and you're done. Too easy.