"> LED´s don´t like current spikes or overtemperature operation. Maybe
I somehow doubt if it is spikes or over current that are causing you problems. LED's can withstand quite large overcurrent spikes, that is how they are run in pulsed applications in order to get higher intensity (short) pulses. They are also normally rated up to +70C at least, so I doubt if it is a temperature problem
You say that they went dim or flashed, that is not a normal failure mode for an led. It sounds more like poor connections inside the led bulb itself. If you can try taking the assembly apart and looking at the joints inside.
Regards Jeff