Around 10:55am the hoist operator noticed a crack in the main block of the HPU for the #1 Hoist. Maintenance called to replace block valve. MSHA Notified at 11:25am. No need for evacuation, #2 & # 3 Hoists were still operational. Block valve replaced, test trip ran and #1 Hoist back up at 12:15pm. MSHA notified of corrective actions at 12:15 PM. (Incident # 1-101114264)