I’ve tried bleach based cleaners but do not want to allow them to soak for extended periods as they will weaken the material. I assume these spot are mildew. They appear while the boat is stored between outings. Is the anything that you can allow to soak and hopefully penetrate the fabric? The fabric is marine grade vinyl and I’ve even used a 3000 psi pressure washer with the current products. Any suggestions that won’t ruin my seats would be deeply appreciated. thanks