Owning a 2014 Impreza, yeah I went thru this also at 132K mikes. Valve body best price was about $800 .... then in FSM says after replacing, check fluid level by ATF temp, then do CVT retrain.
Valve body kit includes a plastic bonnet you put all around AFTER you remove the intake tube, throttle body ( just remove 4 bolts and push to one side ) and the dogbone and bracket to get to top of transmission.
Also FSM has you replace the 2 O-rings on the bottom of the valve body, and retorque to in-lbs the few bolts holding the valve body in place .... in a tight area unless you have a small torque wrench.
Being a mechanic for over 45 yrs, and reading about the successful and a few that were not and wanting this to work for a long time INCLUDING the retraining ( some say it's not required but I follow the FSM ), I went back to dealer I bought the last several Subaru's from and know the service manager ( we worked together in the past ). $1350 for all .... 2 qts fluid, valve body, retrain and all done in a day. GRANTED he gave me a break, but for me it was worth it. Car shifts better than before.
My experience and observations.