Hairline crack in bathroom basin

Hi, we have a hairline crack of about 2 inches in the bottom of our bathroom basin, it had been given a quick repair when we bought our van 4 years ago, appears to be like a mastic substance which has now come loose and never looked a very tidy job. 

Looking for recommendations how to tackle this, someone has suggested trying gorilla apoxy resin, I have noticed various different products specifically for bathrooms, does anyone have any experience or recommendations as to what may be best.

Thanks for reading, Pam and Barry Williams

If you want a professional repair have a look at these people..

http://www.plastic-surgeon.co.uk/repair-knowledge-bank/surfaces/