....my experience exactly.
Once the top layer is worn thru, it seems you get just oxidized aluminum alloy....forever!
The buffer pad turns black, black, black, black etc. etc. never really getting to the point you can start to 'polish'.
...but maybe I was using the wrong stuff?
RV-9a - SOLD!....
kinda missing it!
Lake Country, BC
....paid up til Nov. 2018