Internal lighting sprob. & LWR at Xenon A8

Hello here in the forum

I am the Uwe, driving Audi's for 20 years, but a little smaller calibre (44s), the older one. where the screw has become a hobby. But a problem...
I bought an A8 4D2 that has one (or more) defect(s).
Problem :
Always when light is in operation, the inner handle flickers. , the AI , the knurled wheels of ventilation , the radio etc. the AI stabilizes after ignition . In addition, the info display in the AI also shows a def. or errors in the LWR (Xenon). No light. it occurs only at "door on" driver side, whereby the gr. Interior lamp in front of the interior mirror also only looks dark and flickers, but other doors open at the same time. Driver's door, the error does not occur (speaks it lights normally bright and without flickering). At a phone call with the seller, (car bought 700Km away), said this he had once expanded the left main headlight, but would have been nothing special. My questions are:
Could be a connection, inside. --> Xenon (Xenon --> LWR is clear) ...
how to fix it and does it on its own, or rather work on the workshop because of div. Special tools or RLF for this type.

Is a bite much for the beginning, only if it is too much, I return the car, which would be a pity ...

So thank you very much in advance ...