Hello BW,
Are the black spots a mold or debris. Eitherway, can it be cleaned with a tool or should be sink be completely removed. Any solution can seep in for the complete clean of the mold / debris. The sink has been cleaned every day. However, it is around 2 years from the clean state to below view. Is there anything we have to do during daily maintenance of the sink.

Thanks for your time.
Happy Maintaining your space for positivity.
MM.