I find the fact that you and Dougkelly20, and donglow2 are all "flushers" very interesting. It makes me wonder how many other forum members have had a flush done???
As I have mentioned in my posts, I am not a "lifetime fluid" believer, and will certainly be having a transmission service at about the 60,000 mile mark, but up til now, I have not considered the "flush option." I'm still not fully convinced, but now I'm not 100% against it, like I was in the very recent past. I will be asking a lot of questions to some Subaru transmission experts before I commit either way.
One thing I would suggest to you is that you find out "exactly" what transmission service your dealer did on your vehicle. I know you said that they told you that a "flush" was performed, but from what I have read online recently, sometimes "flush" and "drain and fill" seem to be sometimes used interchangeably depending on which person at the dealership people talk to.
The basic question that I would be asking is "was a flushing machine used on my vehicle?" ... as per the following link
https://www.transmissionrepaircostguide.com/what-is-a-transmission-flush/