Hi,
Welcome to the group, as far as the fuel cap goes, after you have remove it from the tank, with the cap upside down, if you look below the seating area you should see several small blades of metal sticking out into the inside "wall" of the cap, these are part of the inner fastener, that act as spring/grippers, you have to carefully lever them away from the cap a little at a time and work them upwards, the entire unit should come out, but be careful not to strain them.---ken