Taillight Trouble

I have a 2004 Prius with 242000 miles. More than 100000 miles ago I had the dealer replace the driver's side tail light assembly when the LED brake lights died. Recently that same assembly has developed an intermittent problem with the LEDs sometime working properly and sometimes becoming barely visible. I have checked the connector and it's secure. Playing with it and the wiring around it doesn't make any difference when it's either full on or almost off. Does anyone have a suggestions as to what may be wrong before I pop for another new assembly?