Wheel brake leak
CHC incident
An even simpler reason would be a brake line fitting leak.
Park brake on (Offshore landing) would mean a permanent leak of the lefthand system until the low level switch cut off the "non critical" consumers. The accumulator would empty itself out the brakeline, and presto, you have a very interesting scenario on your hands. No brakes, no rotorbrake, and no AP hydraulics.
Torcher