Maybe one of the CFontz guys could give you a better idea of what the cause of that type of display problem is, but it's definately not the LEDs.
I am thinking it may be worth a trip to the auto wrecking yard and get hold of another cluster and use that. Those kind of displays are custom made for the car manufacturer, and you won't be able to source parts from another supplier.
If you went to your car manufacturer for a new replacement expect to be slugged big-time. My day-job is working for a company that manufacturers automatic transmissions for passenger cars, we sell the car company an auto for about $1600-$1800, if you went to the car company to buy a new transmission, unfitted, they charge over $5000. Not a bad mark-up.