Sorry to be a bit of a pessimist but take it from one who was at one time an adhesives chemist, nothing will effect a permanent repair except "welding" the broken parts together with heat. An alternative would be a mechanical fixing of some sort.
I had to repair a broken ABS fixing lug on one of the front sidelights of my BMW 740 Sport recently; I did that by using pins to splint the broken parts together and then burying the pins in polyurethane sealant. The sealant still peels off the ABS but the repair is sufficiently strong to hold it together. (New "crystal" sidelight for the facelift E38 is approx £130!
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