I have a 03 crown victoria p71 and its been misfire on. #5 and #6 for 3years and I have had it at all kind of shop but one mechanic said it could be a seeping head gasket

https://youtu.be/QA7KVQq9vKA Here is a video of scotty doing some test. Follow these steps and it will help you determine if you need a head gasket or not. Hope it helps