DIAGNOSIS A leak from the bottom almost always means the main sealing ring—the large, flat, gray silicone gasket that sits between the blade assembly and the pitcher—is either missing, damaged, or not seated correctly.
FIX Unplug the base. 1) Unscrew the blade assembly from the pitcher. 2) You'll see the gray silicone ring. Remove it. 3) Inspect it closely for any nicks, cracks, tears, or warping. Also, check the groove in the pitcher where it sits for any food debris. 4) Clean the ring and the groove thoroughly. 5) Re-seat the ring perfectly in its groove. It should lie flat and even. 6) Screw the blade assembly back on firmly by hand. Don't overtighten, but make sure it's snug.
IF THAT DIDN'T WORK If the ring looks good and is seated properly but it still leaks, the plastic threads on the pitcher or the blade assembly might be cracked or stripped. Hold the pitcher up to a light and look for hairline cracks near the center. If you see any, the pitcher needs to be replaced.
HEADS UP That sealing ring is a wear item. It can degrade over time with heat and cleaning. If it's more than a year or two old and leaking, just replace it. You can find official replacement sealing rings easily online—it's a cheap fix that saves a big mess.