I have had my wrx for 3 years and 40k miles on it and have just done synthetic oil changes every 3500 miles, I know I should be doing something else by now,
what do I need to do? and what brand or kind of stuff should I use?

I have read on here that I might need
transmission fluid?
rear diff fluid?
anything else, and what kind and where can I get it

 

i KNOW SOMEONE WANTS TO REPLY

 

when you bought your car you should have gotten a maintenence schedule pamphlet. the back tells you everything that happens at scheduled services.

 

Point your browser to my.subaru.com and set up an account for yourself. Once logged in you'll see a link that reads "maintenance schedule" and the site can give you the manuf. recommended schedule AND the dealer recommended schedule from the dealership where you purchased your car (provided they have one that differs from the manuf.).

 

assuming that you didn't do your 30k. then I would replace:
fuel filter, tranny/diff oils, coolant flush, brake fluid.

you can do all of these yourself.