Have you considered that perhaps the PCB board/ light driver has failed?
Disconnect a flasher wire and test with an old worn 9 volt battery to keep the volts and amps low. test the lamps.
If it is the lamps:
here is red grain of wheat bulbs - perhaps a heat gun will loosen the bulbs from the housing. I would hot glue or only a small dab of glue for repair removal.
This is definitely a modeling project to repair this.