Actually, I think you have it the wrong way round and this may still be an issue: Recent piaware (from 2.1-3) and fa-supplied dump1090 have standardised on port 30104 for mlat back-feed into dump1090. So piaware was installed correctly (albeit manually by me). It is dump1090-mutability that needs to be reconfigured to make it listen on 30104 instead of the previous default of 30004.
More info see here:
https://discussions.flightaware.com/ads-b-flight-tracking-f21/piaware-2-1-3-released-t36047.html
I think it is best to stick with the default port of 30104.