Sikaflex EBT. Adhesive, sealant, and filler. Never goes truly hard. I used it for same thing, excellent results. Mask up the area well for good results.
Sorry, it needs to be scraped off first, thats the hard bit. Then use Sikkaflex EBT to re seal. You really need someone to get on the roof to do a "proper job"Just taken mine out as it was leaking badly..and it appeared to be put in with bathroom sealant. Now I can't get on the roof but obviously need to put it back in ASAP so can I put non setting stuff over what is already there? Obviously I've scraped off as much as I can get to