Hatchback main boot lock issue

Ok guys my father in law gifted us his old car as my last car was dying. He used it as a taxi and it needs a general tidy up to take the roughness of it. Although it runs sweet as a nut with 307k miles on it and flew through mot all it need was new callipers allround as the boots where all torn so pistons where knackered. Any way the car was hit in the rear last year but it was very minor damge and it was repaired, but the boot lock mechanism has been playing up so i stripped the rear plastic panel off to investigate as the boot would close then youd hear it pop and it would be sitting slightly open. So as i said i i looked at the mechanism and the only thing i noticed was a "rivet" that goes into the sliding bar (to pull the main lock down and hold it  down) was sitting out . I placed it back into the bar it has sat in place for a few weeks  but it has come out again. So the problem is i cant see any close up pics to see how the "rivet" was fixed in . So has anyone elese had this issue and how did they fix it ? My only thought is an m3 bolt through it?