I have the same problem - the black insert has separated from the sac. Talked to Mike about it, and he said they are heat sealed, so can't be repaired. He suggested that I could try 3M marine sealant if I wanted to give it go before replacing it, but couldn't find the product he recommended. Tried a Sika marine sealant, and it lasted for a couple of weeks before separating again. Will try again and give it another go before giving up
Have a talk to Mike (he is very helpful) and see if he has any different suggestion for you