DIAGNOSIS Odors get trapped in the silicone sealing ring (the gasket) that sits in the lid of the blending jar. Porous foods like garlic, onion, and fish oils are the usual culprits.
FIX Remove the lid assembly. Pop out the clear center piece, then you can lift out the black silicone ring. Wash it thoroughly with hot, soapy water. For the odor, make a paste of baking soda and water and rub it all over the ring, let it sit for 15 minutes, then rinse. You can also soak it in a 50/50 mix of white vinegar and warm water for 30 minutes. Rinse very well and let it air dry completely before reassembling the lid.
IF THAT DIDN'T WORK If the smell is truly baked in, the ring might need replacing. You can order a new sealing ring from Ninja's parts website. It's a wear item, so it's good to have a spare anyway.
HEADS UP Always disassemble and clean the lid fully after blending strong-smelling foods. Don't just rinse it and leave it sealed on the counter—that steams the odor right into the silicone. Storing the lid disassembled also helps prevent mildew smells.