Diagnosis
Leaks from the housing bottoms are classic. It’s either a cracked O-ring, a housing not seated straight, or the housing itself is cracked (less common).
How to Fix It
Shut off the water and release pressure by opening the faucet. Unscrew the leaking housing(s) by hand. Carefully remove the filter and inspect the black O-ring at the top of the housing. Look for nicks, twists, or debris. Clean the groove it sits in. Lubricate the O-ring with a tiny bit of food-grade silicone grease (not petroleum jelly) and re-seat it. Screw the housing back on by hand until snug, then give it another quarter-turn with the wrench. Do not overtighten—that can crack the plastic or distort the O-ring, causing the very leak you’re trying to fix.
If That Didn't Work
Inspect the clear plastic sump (the housing itself) for hairline cracks, especially around the base or the threads. If it’s cracked, it needs to be replaced. Also check that the filter is the correct length; an overly long aftermarket filter can prevent proper seating.
Heads Up
Always have a towel or small bucket handy when you service the filters. There’s always a cup or two of water left in those housings that will spill out when you open them.