I had a similar issue, I used E6000 glue and two pieces of abs behind the crack, I then sanded the crack a little to open it, filled that with ABS paste, waited two days and sanded then covered the whole area with bondo, sanded primed and painted, has not failed so far. I do try to be as careful as I can now to get my arms inside the openings, it's just one of those places which takes a lot of strain.