canberra mishap

finally after 3 yrs lingering on the shelf i decided to have a go the canberra, all that was needed was a last matt finish and the geat doors. Now the problem, i found a crack on the trailing edge just close to the jet exhaust, any major filling and sanding are out of the question as at this point it will not be possible to match the colors. managed to fill this crack anf did the final coat and.............. Found another 3 cracks on the trailing edges, it is literally breaking up, and if find another crack i am going to blow it up

Something must have chemically effected the plastic of the model. I don;t think that you can solve that problem. I would try to fix the existing cracks and if more develop, forget it. Who knows what is effecting the plastic. It could be the paint, the varnish, or something else.