No probs at all. Unfortunately as cars get more technology focused the more features will become subscription services. I saw an article where bmw were looking at doing this for heated seats and other features that would be activated at a cost through the infotainment screen.
You e done a great amount of diagnostic work. You could change the light units or the harness I appreciate the latter you found no corrosion though. Or a diagnostic check.
Welcome to the forum Ben, you'll find the members on here are a friendly and helpful bunch 🙂 whst a great story. I hope you get the Quattro sorted soon. My uncle had a Volvo 480 which he wrote off when he hit a bridge.