Pump body or unions leak at the threaded connections.

Safety first: Turn off pump and relieve system pressure before loosening unions.

Step-by-step checks:

• 1. Tighten unions: Hand-tighten union nuts on suction and discharge. Do not overtighten with large wrenches on plastic fittings.
• 2. Inspect O-rings: Open the union, inspect the O-ring for cuts or flattening, and replace if damaged.
• 3. Check for cracks: Examine the union tailpieces and pump ports for hairline cracks; replace any cracked components.
• 4. Use correct sealant: For threaded connections, use PTFE tape or appropriate thread sealant; do not apply sealant to union O-ring faces.