Small cracks at the pool lid may be fixed with epoxy. If your pump enclosure has become brittle with age and sunlight exposure, the fix will probably be temporary. When the plastic casing is in good condition, the epoxy should seal the leak, saving you a costly repair.
Organizing the Lid
You must remove the lid out of the filter and seal the leak from the interior. Since water pressure pushes outward, a repair from the outside will eventually get pushed outside. Completely wash the lid. Split a V-shaped groove into the crack on the inside of the filter lid.
Seal the Crack
There are two kinds of epoxy appropriate with this repair. Thin, two-part epoxy works well for small hairline cracks. For larger cracks use a putty type epoxy. Thoroughly mix or knead the epoxy. Fill the groove and crack with the epoxy, enabling it to overflow slightly. If you are using putty epoxy, push it in the crack and level it out with just a little overflow on either side. Leave the lid to dry and cure for 24 hours before reassembling the filter casing.