Its fixed. Looking at the brake lever from the rear of the mower, I found that pushing the lever to the right, rather than forward, also locks the brake rotor. The lever is mounted on a threaded shaft and secured with a nut. I tightened the nut which moved the lever towards the right which locks the rotor. After a little experimentation, I found the right amount to tighten the nut and it now works perfectly. Locks up good and with the brake pedal and no drag when the brake is released.
P.S. FWIW I later looked up riding mower brakes on you tube and learned how they work and how to adjust them.