This is one of those tricks everyone should just know, so I'm sharing. When your refrigerator or freezer shows signs of a weak seal - (those mildew spots where air and moisture get in/out or when you shut the freezer the refrigerator door sort of puffs out and then back again).
This can happen to even new appliances. One seal will be very strong the other a bit weaker.
When you wipe the gasket down during general cleaning, dry it off and take a bit of vasaline and rub it on the gasket. It is amazing how much tighter the seal is. Reapply as needed.