I have a 2000 legacy wagon, same series as yours. I've used Mobil1 transmission fluid (coupon advance auto) with a new spin on filter with each change at 25,000-30,000 since 25,000 miles. I have 214,000 miles and no transmission problems, no slipping, nothing. Fluid looks brand new. If you change the filter too, you get almost six quarts out. I won't use anything else, Mobil1is about $6.50 a quart after coupon. I also live in the mountains and the terrain is very hard on tranmissions. It snows too and there is lots of slipping around. The local Sube shop (just work on Subarus) said my transmission had gone the longest they had seen without a rebuild.