B737 Captain reported ground personnel advised his left main landing gear was on fire after setting brakes at gate. Captain reported that maintenance observed a fluid leak from brake line and no apparent burn damage after CFR personnel sprayed the gear area.

Narrative

After taxi in and with the parking brake set I noticed decreasing hydraulic accumulator pressure. The hydraulic accumulator dropped quickly to approximately 1;000 psi. We checked the hydraulic system and hydraulic system B was below RF. I opened the Captains window to ask to be chocked; then the ground crew informed us that our left landing gear was on fire and relayed that they had called for the fire equipment.I had the First Officer request priority handeling with ground control and call for high priority equipment and fire trucks. The First Officer reviewed brake fires and all possible situations associated with a brake and hydraulic fire. Within a few minutes the ground personnel said the fire was out and they had chocked the nose gear. The firefighters sprayed the area and kept everyone clear. The ground crew plugged into the intercom system to relay information and I reconfirmed that the fire was out. During the event I notified and briefed the flight attendants and passengers. Our situation had stabilized as we continued to monitor and no evacuation was needed. When it was safe the firefighters allowed the Jetway to be brought to the aircraft for deplaning. We made maintenance write ups of the issues; then discussed the issues with maintenance. Maintenance said that the brake line was leaking hydraulic fluid which was the cause for the smoke and fire. When we looked at the left main gear after the event it did not look like anything was burnt. I suspect that what the ground crew saw was smoke. The crew was debriefed and later informed the Manager of the event.