K2543 temperature - damage?

I installed a k2543 kit 6 volts in my oldtimer. The engine started immediately. After a few moments the engine stopped and I forgot to turn the ignition key. So the 6 volts was still on the kit and I did not yet mounted the heatsink. So the kit and certainly the T2 became very hot. Now the engine cannot be started anymore. Which part(s) of the kit could be damaged?

Difficult to say. Most likely the power transistor.