Rear Tail LED Lighting

The left rear LED taillight on my 2009 Audi A3 – 1.4TFSI is no longer working. Both brake and indicator working. Likewise the LED light on the light cluster on the rear tail door is not working. Reversing and fog lights all working. Got in touch with local Audi dealer and advised that car will have to be attached to diagnostic machine to identify what is the issue (€90) and may require the replacement of both light clusters. This seems excessive for the possible replacement of 2 x LED lights! Are the LED lights built into the light cluster and can only be replaced with new one’s! What are the possible faults and repairs required? Could I be looking at a cost of up to €300 to have this repaired?