I have had front loaders for 10 years and my parents had front loaders for probably 30 years and none of these washers have ever had mold issues. You do need to leave the door open several inches and not just cracked so that the water can evaporate. Once the seal is dry you can close it and just leave a crack. You can speed up the drying process by drying the seal with a towel.
Check the grooves in the seal for lint. Lint buildup may not completely dry and can cause mold and odor build up.
You also need to be sure to not use too much detergent. Always use HE detergent. The foam, even when it's not visible, leftover from detergent attracts spores, bacteria. If there are bubbles on the seal when you remove your clothes all of the detergent may not be washed out. If you line dry an item and it's stiff it still holds detergent.
Use less detergent than the product tells you to use. I use about half the amount. If you have hard water use a powdered water softener along with the detergent.
Are you sure that the seal still has mold on it or is it just the stain? Mold does stain. Once the mold is removed the stain does not smell. My seal has folds in it. Have you stretched out the seal to clean in the folds?
You can also purchase a new seal and have it installed. I suggest talking directly with a repairman who services the brand of washer that you have.
I love my front loader! My clothes are usually lightly soiled and they get clean using the express wash. I do usually opt for a extra rinse. They spin much dryer and take less time to dry in the dryer.