Hi, yesterday I bought an 07 Fit Sport (automatic) with 112k miles, and the seller said that I should probably change the transmission fluid, since he had no idea when it had last been done. Should I just change the fluid, or should I do a full transmission fluid flush?

 

Just drain and refill it. Honda does NOT endorse any sort of flushing via machines or chemical flushes.

You can try the 3 time ATF drain and refill along with replace the in line ATF filter on the back side of the transmission under the airbox (Part number - 25430-PLR-003) if you want to get the ATF good and clean.

Other things to consider at that mileage aside from of course fluids and dampers/struts/shocks... Valve adjustment, spark plug replacement or torque check (They like to back out over time, use S2000 spec of 17 to 20 lb ft).

 

Great, thanks for the info. It has a rattle that you can hear most prominently on the passenger side that stops when you hold the muffler, and my friend just mentioned that valve adjustment could have something to do with that.