Diagnosis
Food debris and liquid have seeped into the gap between the rotating cup lock ring and the stationary base housing.
How to Fix It
Unplug the base. Hold the base firmly and manually rotate the black locking ring counter-clockwise. This exposes the sealing area. Use a damp cloth or soft brush to wipe away all residue from the ring and the base housing. Rotate the ring to clean the entire circumference. Rotate it back to the start position.
If That Didn't Work
For dried-on residue, use a cloth dampened with a mild soap solution. Do not submerge the base or run water directly into it. For persistent sticky material, a cotton swab with a drop of dish soap can be used carefully around the seal.
Heads Up
Prevent this by always ensuring the cup and blade assembly are clean and dry before locking onto the base. Wipe the base's sealing surface with a dry cloth after each use. Never immerse the base in water or place it in a dishwasher.