I just got back from the dealer, having a "shimmy" in the rear end checked out (loose bolt on endlink, fixed). I asked him about changing the transmission fluid, as I am over 20k miles (the Subaru service manual reccommends a change at 15k for hard use, 30k for normal).

He said that he would wait until 30k, and in fact changing your transmission fluids at any interval under 30k is a bad idea, because all transmission fluids have a "detergent" base that can actually erode your gears and synchros. This detergent effect goes away after the first 5,000 miles or so after a change, but if you change often you might be changing it before the detergent effect goes away -- greatly increasing the wear on the transmission.

I find this information really interesting, considering that he COULD have charged me $299 to change the transmission fluid (labor + fluid + tax) and instead passed on making the money! He had me right there, ready to have it changed, and he turned me down -- obviously this show of honesty impressed me, but the information he gave me is some food for thought as well. Anyone care to debate it?

 

Hmm. Dunno about the detergent thing. They did mine at the 30k service, but its cool that your dealer suggested waiting rather than reaming you now.

I did notice that, after the fluid change, it takes longer for the gears to spin down. I now make sure I press the clutch a couple of seconds before I engage 1st gear when stopped.

 

Interesting. They changed mine at 15k on my my04 and i'm now having 1st gear grinds where i didn't before.

 

Yup, same here and for a couple of my friends. Its not that the transmission has suddenly changed, but I suspect the fluid that the new cars ship with is more viscous than the replacement stuff. Its annoying, but I've got used to working around it.