Had the same fault as you recently with a Polo. Misfire Cyl No 1. Removed the head and even though everything looked alright, I poured petrol on the valves and cylinder No1 exhaust valve leaked quite badly. I could not see anything wrong with the valve or seat. Sent the head to a machine shop for pressure testing. He said he got a lot of these from 2 VW dealers. The valve seating is the problem . Re cut the valve seats and replaced all exhaust valves. Engine is purring like a kitten now. Hope this helps.