On my 1991 Montero LS my key will lock and unlock it but when I go to the interior switch the unlock button works but the lock button does not. I took the door panel off and it looks to seem like everything works. My back 2 doors wouldn't open so I took the door panel off and sprayed the mechanism with WD-40 and it worked. I sprayed the cargo door mechanism with WD-40 and the switch still wouldn't lock it. Any suggestions on what i should do?