I Have A Frigidaire Front Loader And The Gasket Is All Black With Mildew.

Vinegar is the safest way to remove mildew, but not as effective as other methods. Bleach works great, but it will dry out your gaskets if you use it too many timess. WD-40 works well, but not as good as bleach. 

Hydrogen peroxide sprayed on the gasket will work, but you have to be sure to remove all traces of it after your done. That advice applies to bleach and WD-40 as well. Do not leave any of the cleaner on the gasket. Clean it up with soap and water and wipe dry. 

Once mold or mildew has stained plastic or rubber, you will not get rid of the coloring. You can sanitize it with bleach and water, but you will not get rid of the spots, or discolored areas. You would need to purchase a new gasket for the front load machine. Then once you begin with a new seal, I would strongly suggest to clean or sanitize the inside of the unit's drum. You can use the sanitize, or any hot water setting, throw 1 cup of bleach into the drum and wash with no clothing inside. Then after every cycle leave the door cracked so the moisture can evaporate and prevent mold from forming. It is stated in the Owner's Guide to clean the door seal with a cloth and even bleach or vinegar to help keep mold spores from forming. This is always a concern when you have an appliance use water, and when the rubber seal (gasket) has multiple areas within it for gravity to pull water down into.

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