JLG 33HA Basic: Swing Drift/Swing Break Doesn't Engage

Hi Guys. I'm troubleshooting this lift for my boss. Hydro Mech is not my area of expertise. It's an old lift, and the swing drifts a lot. It has a swing break that doesn't seem to engage under any conditions. It did engage once this morning, however, but I'm not sure what we did to make it do so and I haven't been able to make it do so again. It looks like a single caliper with two pistons that bites a rotor which is part of the swing gear assembly. The caliper appears to have one hydro line going to it.

Can someone tell me when a swing drive is supposed to engage? Is there a switch or solenoid that engages it?

JLG does not have a manual for this lift online.

Any ideas on what the possible points of failure might be?

Thanks so much,

Matt.