The "U" shaped aluminium heatsink has the triac (the part with three legs) bolted to it. The triac "legs" go through 3 holes in the PCB and solder to the copper pads on the bottom side to make electrical contact.
The aluminium heatsink has three tabs that poke through holes in the PCB as well and can be (moderatly) secured by slightly bending them however this rarely holds them firmly.
It is common for these parts to be knocked/bumped and break away from the board - sometimes damaging the tracks and maybe breaking the legs on the triac.
EDIT: changed transistor to triac after looking at a three flipper DE PCB I have here. From memory the triac is used to hold the coil in the activated position (low power coil) so your flipper should still activate BUT not hold in??
