PAS fluid is something that is changed, but on a much more infrequent basis - more like brake fluid. (mechanics.stackexchange.com)
In either case, rebalancing tends to work best when done on a relatively infrequent basis. (sec.gov)
Anyone who reads this Dog Blog on an even infrequent basis will know I am a firm advocate of Raw Bones as the ideal way to naturally clean Dog's teeth. (thethreedogblog.com)