My question is how hard is it to do and any recommendations on what to use.

I've had people tell me quite a few different things as far as fluid goes.

All I know is my gears are grinding and things are feeling really rough in general with my shifting. I want to get some new fluid in there before I loose another syncro or blow a gear.

 

Throw in some synchromesh for the grind.

Changing the fluids isn't that difficult at all.

 

try searching on nasioc.com for uncle scotty's cocktail. I've never actually used it but alot of people seem to like it.
Another mix I found while researching on nasioc.com is syncromesh with regular transmission fluid. That is what I'm using right now and it made a world of difference for my 02 transmission. Before the syncromesh/regular transmission oil combo, I would sometimes grind going into first gear from a complete stop with the foot on the clutch.
As far as changing it goes, its pretty straight forward, just open the drain plug and drain out all the old fluid and remove all the crap on the magnet, then fill it through the transmission dip stick tube and check fluid level with the dip stick. The transmission dip stick tube is under the intercooler on the passenger side in case you're not sure where it is

 

Thanks. I'll do the search. I figured that's all there was to it. Just never done it on my wrx before.

 

i just did my rear diff fluid on my 99RS yesterday. it was a joke. took out the rear lower plug with my 1/2 ratchet. drained all the fluid.

cleaned the plug. put the rear lower plug back in and tightened it by hand.

took out the upper rear plug. cleaned the upper rear plug. pumped in fluid until it began spilling out. put the upper rear plug back in.

done!

i'm going to do my transmission fluid this weekend. i'll report back about that...

 

Pull the intercooler (makes it easier to get the funnel in the dipstick hole. Jack up the car. Pull the drain bolt on the transmission (set aside and clean). Grab a 1/2'' breaker bar or ratchet and pull the fill plug on the differential, Then pull the drain plug. Once everything is drained reinstall drain plugs on transmission and differential. Fill transmission (i believe its 4.6 quarts), fill differential, may need to have a pump. or you can use the squirter from the top of the gear oil bottle. Fill the diff till gear oil starts coming out of the fill plug hole. Put the fill plug back in. Drop the car, throw the intercooler back on. Put the dipstick back in Drive around the block and check the transmission for correct fluid level, and your done.

Pretty much the jist of it. Not to hard but it takes a little bit of time.

 

and my apologies for not reading your original post earlier.

i've used the standard fluid, some 'unknown' stuff that was thrown in when my clutch was changed out, redline and now swepco.

honestly, swepco has been the absolute best so far. i'd happily recommend it again, and buy it for all of my cars.

 

I used plain ol non-synthetic 'Stalube' of the proper viscosity on my old bugyeye wagon...I think its GL-5 75-90. I had ~65K of hard driving and it never grinded unless I mis-shifted. I never recommend synthetic in the wrx tranny, my buddy used Mobil1 and that thing would grind in first...even at a dead stop, clutch to the floor, it sucked.

Changing the fluid is easy, just like the motor oil, drain and refil (although the read diff drain bolt may be a pain, just use some muscle.)

 

i was told sti and wrx uses different factory fluids but this is what i did for my 05 sti.

I used

Rear Diff: part#KO305Y0900 'Lsd 1 Liter' (subaruparts.com) x 1 container
Front diff/transmission: part#RL875S 'Redline 75w90ns' x 5 quarts.

For tools, i used siphon pump for rear diff oils and funnel with long extension so i didnt have to take off the intercooler.
i dont remember the socket sizes but i had sensor on the nut of the rear diff. i did break it when taking it out, used some 2-part glue then was good as new. other than that, it was all very easy, cleaned out extra fluid by sticking my finger in there (with gloves) and push the fuilds out.