Black spots on our slide out rubber seal

New TT owner (2008 kz spree) and there are black spots that look like mold on the slide out rubber seals. I tried diluted bleach on a small test spot but it only helped a little. Does anyone have advice on how to clean this? Total RV newbie! I do have the conditioner for the rubber for after cleaning but just dont know what to use to get those black dots off.