035 133 554 - ''insert for injector''
You need to unscrew the brass part from the top with a 13mm hex head. This is a pain in the arse, as i couldnt find anywhere selling the correct size hex head, so i packed out a 12mm with leccy tape. once you undo that it should all fall straight out. I would recommend replacing your injector seal at the same time for the small expense.