You cannot use bleach on carseat harness straps, or the plastic. In fact you cannot machine wash the straps, nor are yo usupposed to submerge them in water. The bleach and water sumbersion will damage the fibers in the harness, making it very weak and susceptable to snapping in an accident.
Mold is also quite the health hazard.... I would purchase a new seat. You just can't guarantee that the mold is totally gone with the way you have to clean the straps......
so its either damage the straps by using harsh chemicals or machine washing them and making htem dangerous, or exposing your newborn to mold.
You can purchase a new infant carrier at Wal Mart for $40. KMart is having a carseat sale right now, 20% off. Maybe a family member or very close friend has one you can borrow that you can guarantee isn't expired or been in any type of accident?
If it were ME, I wouldn't question it, I would purchase a new seat. ITs just not worth damaging the straps trying to clean them, nor is the mold worth my babys health.