Toro Tumecutter Z4200

I have a Timecutter Z4200 z mower, approx 11 years old.
model 74360
S/N 270000276
When I stop driving and the levees are out (brake on) the drive is still engaged, very slowly but engaged. Seemed like the brake is not engaged.
I took the rear wheels off and see that the brake is slipping on both sides.
not sure is I should try replacing the disc brake or brake arm kit #59 and 53 in parts diagram. They don’t appear to be stripped.
Anything I can check prior to purchasing parts?
Thanks