How to clean the shower screen sealant??

[oliveroses]

Hello! Our shower screen is a double piece of glass that is hinged in the middle. I'm trying to clean the plastic seal between the bottom of the screen and the edge of the bath, as it has developed black spots underneath. It's on the part of the screen attached to the wall, so there's hardly any movement/give in that part of the screen.

I can't get a toothbrush or its bristles under the plastic to clean it. I can get a thin piece of plastic underneath (like the narrow end of a tooth flosser) but that doesn't rub the stain, just moves any debris (yuck)

Any brilliant tips? It's driving me mad!

Sorry for boring post

I tried for DECADES to clean it effectively, with very little results. I tried to push the water in using all sort of small brushes, soak in bleach,....
Then realized it's a very inexpensive thing to replace: I just buy a new off ebay every few years (you can cut it to measure) and the job is done:).

@user1471523870 thank you - that had never really occurred to me. Good idea!