starter problems
 

hey guys.... a while ago my car wasn't starting so i kept on putting in the ignition switch trying to crank it. after more than 20 tries it finally cranked. each time there was one audible click (from the starter i guess) after that it worked for about a month

then all of a sudden i would hear a click on my first try then it would crank on my sencond try. i figure its the power bolts on the starter....i take them off (power and ground) and clean them with a metal brush.....works perfect for a month

samething happens and so i clean off the terminals and this time put a little grease.....after two weeks same thing happens. but after i hit the selenoid with a hammer it will start up for the next 20 times on the first try.....

wtf is it? my cables? or my starter has gone bad....should i just replace it? or clean off the terminals again