There are many interesting cases where great composers of the past have made obvious changes to eliminate parallel 5ths and octaves, mostly for the better, but occasionally out of guilt and for the worse. And numerous examples where they left them in for valid reasons. As I think I mentioned above, Brahms made a collection of such with comments, and Schenker published this with further explanations. This little volume makes very interesting reading in the English translation by Paul Mast to be found in vol. 5 of The Music Forum (Columbia University Press 1980)
Here are couple of parallel octave examples by Beethoven that Brahms found “unpleasant”:
