NEED HELP Door won't stay shut on 2005 mazda3
 

I just bought an 05 mazda3 GT Sedan. When I close the driver's side door it just bounces right back at me because the latch won't engage to keep the door shut! I've tried locking the doors etc but that does nothing. Once in a while it will close and engage but then a day later it will not close properly.
Do I just need some WD40 or should I take the door panel off and replace parts?!?
I can't drive it until I get this sorted out!

if u can get some white lithium grease try and spray the latch and try to use a screw driver to move the latch alil bit to work in the grease if u cant do that whie its in the door then ur gonna have to take the latch off and try it that way. do that before you try and by new parts