Picture of Change the differential fluid in a 1999 Subaru Legacy
The Legacy manual specifies changing the front and rear differential fluid every 30k miles or 2 years.  This Instructable will demonstrate how to do this for a 1999 Subaru Legacy and should be similar for other years as well.  I completed this maintenance on my car at the Menlo Park TechShop and appreciated the extra space and tools in the auto-bay (I made it at TechShop).

Step 1: Gather Tools and Supplies

Picture of Gather Tools and Supplies
The tools I used included:
breaker bar
17 mm and 19 mm sockets
torque wrench
fluid catch basin
rags and news paper
kitty litter
turkey baster
four jack-stands

For supplies I used:
differential fluid (3 quarts of 80W-90)
new washers (not shown)