I have an Audi A6 Avant, manufactured in 1998, with the AFB engine.
The MFA (Multi-Function Assembly) will become darker at warm temperatures or after being in operation for a while.
Completely black in color, especially during the summer.
Do you have any ideas for a cheap repair?
'Cost-effective' is a broad term, but a new display can be installed for a price range of €150 - €250. For example, with companies like these: http://www.tachopix.de/mprices.xml?!, or Mr. Felske from the Netherlands: http://www.tacho-felske.de/5003.html.
Or, at an auction house, you could bid on and acquire another one with a fully functional MFA .
Here's another page with somewhat more moderate prices. However, I haven't tested any of the ones mentioned here, nor can I say anything about their work. Please keep this in mind.