On my M6060 there are 2 vent lines, one goes to the rear of the cab and is squeezed down a bit. The other is a little larger and the rubber hose is connected to a metal line that runs to the top left of the cab to what appears to be a filter of some sort. The tractor started acting like it had a fuel restriction and I blew that filter out as much as I could getting a lot of dust out of it. It ran good till I was round baling some dry, dusty hay yesterday and it did it again on the way home. Question is, there are 4 what look like knobs on the cover, are they screws and will that cover come off? Thanks, Keith