DIAGNOSIS The exit needle or the K-Cup holder seal is compromised, allowing grounds to bypass the filter.
FIX Inspect the rubber seal inside the K-Cup holder door. Remove any debris. Clean the exit needle in the top of the holder with the cleaning tool. Ensure you are not using damaged, off-brand, or reusable K-Cups with torn filters.
IF THAT DIDN'T WORK The puncture needle assembly at the top may have a cracked housing. Visually inspect for cracks. A cracked housing allows grounds to leak around the needle. This part is not user-serviceable.
HEADS UP Do not over-insert the cleaning tool into the upper needle. Excessive force can crack the housing, creating the very leak you are trying to prevent.