I just bought a Foton 404 with the SL3105BT engine. This site has been great showing tricks to help with the tractor. I have changed all the fluids in the tractor except the oil in the injector pump. I found on an old page that you fill it by removing the little mushroom shaped thing on the top of the pump. I tried turning it and pulling up on it, but I could not get it to come off. How do you remove this vent to fill the pump?