Diagnosis
The issue is in the angled grease chute and the cup. Grease cools and solidifies in the chute, creating a blockage that causes backup and leakage at the cabinet joint.
How to Fix It
Empty the grease cup. Remove the entire chute assembly from the grill body. Soak it in hot, soapy water to liquefy the grease. Use a long, flexible bottle brush to scrub the inside of the chute. Ensure the hole from the grill basin into the chute is completely clear. Reinstall.
If That Didn't Work
The cabinet leakage indicates the silicone gasket between the cook chamber and the grease chute flange has failed or displaced. Inspect this orange or black gasket. Reseat it or replace it if torn.
Heads Up
For long cooks, pre-warm the grease chute and cup. Before starting, place a cup of hot water in the grease cup. The heat helps keep the initial grease flow liquid, establishing a clear path.