Remove the paint inevery point were the terminals touch the block, frame or body, i put the 3 grounds, battery-engine block, engine block-frame, battery-body, look at the cables they might old and rusty or even broken if all of that has been done and the starter keeps giving you problems take it apart and take a look inside watch and the part in the center tha things that spins dont know what its called and if it looks like marked you will see it right away then its bad.