Make a loose paste with TechnoFresh®, salt and, dishwasher detergent.
Note: Some of the new dishwasher detergents are not as effective as they used to be. They no longer contain a lot of phosphates for environmental reasons. If possible use a powdered dishwasher detergent. Or use the cheapest brand you can buy. You won’t pay for fancy rinse aids, enzymes and other stuff you don’t need that might hinder the cleaning..
Use equal amounts (say - one ounce of each of the 3 items) with hot water.
Put on some plastic gloves. The mold and bacteria slime are really yucky.
Wet a small rag in hot water and scrub the paste onto the gasket until it becomes a pasty mix.
Try not to dilute it too much.
The slime coating should break down and the mold underneath should start dissolving.
Scrub the treated area with a small scrub brush or sponge scrubbie
Repeat procedure to smear loose paste on gasket
Place a wet rag on top of the gasket to keep the area wet (more than damp).
This procedure results in a very, very strong concentration of the active chemicals right at the surface.
Let it sit for at least 8 hours lightly scrubbing every now and then to get fresh pasty solution to the moldy surface areas.
Contact time between the paste and the mold and slimy bacteria is very important. This is to make sure the chemicals have time to penetrate and react with the nasties.
When done, scrub off as much of the dead black mold as you can, then rinse clean.
This should remove all the nasty stuff on the surface that could otherwise contaminate the laundry. It has also removed the slimy coating that was protecting the nasties.
You should now have a gasket that has a clean surface and possibly some light gray stains in the rubber