My '86 5kCSQ has the standard Audi radio by Blaupunkt. The volume control has become noisey and intermittent. I would prefer to replace just the volume control but have not been able to locate any source of replacement parts. Does anyone know where I can get radio parts? George Simmons '86 5kCSQ 150k miles '91 200TQ 20V 75k miles '94 S4 22k miles