Step 1: Wash the whole car as best you can.
Step 2: Use an iron fallout remove and tar remover on the whole car, leave for 5-10 mins then rinse.
Step 3: Clay the whole car, including the glass - this should remove what ever is on the windscreen.
Step 4: Rinse and dry the car.
Step 5: Polish the whole car, including the glass (you can get dedicated glass polish for this)
Step 6: Use something like CarPro Eraser, which is IPA - this removes any last protection or any polishing oils, and leaves you with perfectly clean paint.
Step 7: Apply LSP of your choice.
Also - see this thread for a detailed walk through and recommended products
https://forum.abarthownersclub.com/index.php/topic,92.0.htmlBertie