gas gauge problem & oil leak

my gas gauge jumps from full to empty back in forth. i dont know why. i dont think its full...since i just put a few gallons in to see if it would shut the pump off, but no luck.

also, is it more likely to have the oil pan gasket leaking or the valve cover gasket leaking worse? there both leaking i just cant tell which one to fix first (probably dont have time or $$ to fix both at the same time)

thanks