Then there is no problem with the insulators and mounting hardware.
Test each transistor with the diode test function of your meter. You can leave the red wires connected or remove them, it doesn't matter. Pull the black connector plug and note which pin the blue wire was connected to. That pin is the base. The yellow wire connects to the emitter.
Test by putting the red lead to the base pin and then touch the black lead to the emitter pin and then the collector mounting screw. You should get a reading of approx. 0.6 volts on the meter with both connections. Next reverse the two meter leads putting the black lead on the base and touch the emitter and collector with the red lead. You should get an open reading on the meter (the same as when the two leads are not touching anything).
Finally test the collector to emitter junction by touching the red lead to the collector mounting screw and the black lead to the emitter pin (yellow wire). Also test by reversing the two meter leads. In either test, there should be an open reading on the meter.
Something to watch out for is the fact that on these chassis', the two output transistors are mounted in 180 degrees from each other, that is the emitter and base pins will not appear on the same side.