I am not sure that is pad build up.I can only offer my experience with my 2003 Outback and my 2021 Ascent. The Outback wagon was very versatile lots of cargo space. I had 27 bags of wet heavy mulch in it probably not my best idea. Issues I had with that car are not applicable to you and newer generations. I will say my current Ascent and some current fa24 engines are experiencing leaking oil pans. Dealer tried to blame it on my Fumoto not being torqued enough…which is a joke. My Ascent’s brakes are horrendous for vibration because of pad buildup. Three dealer brake jobs in 36k. May not pertain to Outbacks but very annoying
Generally Japanese vehicles come with undersized rotors and quality is really not that great. They are not high carbon rotors and if vehicle is heavy, they can’t sustain that much heat. Same happened on my Sienna and EBC rotors were definitive solution. There was same talk about pad buildup, but it was rotor issue.
European vehicles don’t have that issue. So, I was surprised that my Atlas started to behave same, although rotors are definitely sized properly. However, VW went same route for the US market on these appliance vehicles. So I had vibration issues and bought OE rotors, which had Brembo stamped on them. They very very light in color, which indicates low carbon content, but whatever. It took them 6k miles to start vibrating. I brake with engine all the time, but I do drive hard to the limit. Also, I put OE pads. They have phenomenal bite force. On Atlas forums it general consensus is pad buildup. I wasn’t convinced.
Anyway, aftermarket rotors are not common for Atlas like for other VW’s like GTI or R where you have cottage industry of aftermarket parts (talking about good stuff). But, ATE (which is my go to brand for anything brakes) just released aftermarket rotors. So I ordered and they are clearly darker. Left old pads (to see if they will cause buildup).
23k later they work like a charm!
I don’t think ATE makes aftermarket parts for Subaru, so I would try EBC rotors in your case.