Oily leaks usually come from hot food and dirty seals

Oily leaks around the lunch box seal are almost always from hot food, an overfilled container, or a greasy gasket — so fix those before buying a new box.

That thin little oil film can sneak through any rubber gasket if the temperature is high or the container is packed to the brim. Heat builds pressure and thins the oil, and then it’s just looking for a way out. Plus, if the seal itself has residue on it, it won’t make proper contact. So: cool your food before closing, leave a little headspace, and wipe the gasket dry every time you wash it.

If you’re still getting spots, stop putting the oily thing directly in the box. A small silicone cup or even a paper towel-lined bag catches the grease and keeps the seal clean. That’s not a workaround, it’s just how you pack lunch.

The gasket is fine. The oil is just smarter than you thought.