I read your post about your 2008 4S. I have same car, same problem. I bought as CPO in 2014. Warranty expires in November. The have replaced the OAS, coils and plugs. My service adviser mentioned potential problem in cylinder 6 as you describe. I don't know why they didn't just fix... But not going to let them allow it to slide with "it's normal" responses beyond this month. What was the final outcome of your fix?