I've had this dashboard computer glitch on my 98 A4 TDi for months. The brake light bulb out warning light comes on and the dreadful chime intermittently, probably 3 or 4 times on a 50 mile journey. Yet no bulb is out and the brake light switch has been replaced. Any Audi specialist cooected it to their computer and said they couldn't find anything wrong so it must need a new computer, but I baulk at paying out £500 for that and was wondering if anyone could give me a second opinion. Also is it true what I read in the paer the other day, that modern diesels will work quite happily on an equal mix of derv and vegetable oil?