I had a similar issue with my skylight over the kitchen. Corners cracked pretty bad and was leaking onto the counter. I always carry a tube of dicor so I used that to seal it temporarily. Once I got back home, I measured the old skylight while still in place and ordered a new smoke polycarbonate skylight and not one of those useless UV eating vinyl ones. Do it right, there are Youtube videos that step by step, just Google it. Took about hour and a half to uninstall old skylight then clean it right, and install with the right stuff. There are many who say not to use Dicor, but it is recommended to use Surebond SB-140 and finalize it with Eternabond tape as I used the 4" white. It made for a very clean final install of the skylight with the tape. I am in the process of ordering a new PolyCarbonate skylight for above the shower now, and will use the same process before I have the same issue. An ounce of prevention is worth a pound of cure.