Hi i am changing the glow plugs on my 2000 2.7 t d i lwb, ihave taken off the inter cooler as the download and on the buzz bar instesd of nuts there are like plastic screws, or are these just covers over the nuts and thread . I tried unscrewing them they have a slot for a screw driver and are round but don,t move ,are they just covers to prise off, or are these the actual nuts. help please, need to get the old girl back on the road.